I do not know, but it is on the surface at least surprising.
AMLO is the nickname of Andres Manuel Lopez Obrador, the President of Mexico since Dec. 1, 2018. Only yesterday, along with Mitch McConnell, President Putin of Russia and President Bolsonaro of Brazil, AMLO congratulated Joe Biden on his victory over Donald Trump in the US presidential eleciton, leaving only North Korea's Kim Jong Un still not recognizing Biden's victory among world leaders. Putin and Bolsonaro and Kim have all been personally close to Trump, with Bolsonaro also imitating him in terms of policy positions. But what is with the delay by AMLO, especially given that polls have long shown Trump having the lowest popularity rating in Mexico of any nation in the world, down around 5%?
Besides Trump's massive unpopularity there are other reasons one might not expect this delay on AMLO's part. One is ideological, although Kim Jong Un is a left wing Communist supporting Trump. But indeed, even though he started out in the centrist PRI, AMLO has long been identified as the leading left progressive figure in Mexican politics, running as the presidential candidate of the main leftist party, the PRD, in 2006 and 2012 (Mexican presidents serves single six year terms), then starting his own party, MORENA, which he ran from successfully in 2018, although in that year he did have the support of a minor socially conservative party.
There is also the matter that there have long been differences over migration policy, with Trump's anti-Mexican immigration policy extremely unpopular in Mexico, along with his wall, and certainly his ridiculous demand that Mexico pay his wall on the southern border. Trump even threatened AMLO with punitive tariffs if he did not help Trump out in slowing migration from Central America, and AMLO caved and went along with Trump's demands on that.
There have also been differences over joint operations against drug gangs and corruption, with the recent arrest in the US on drug-related charges of a former Mexican defense minister, Cienfuegos, creating a diplomatic hullabaloo. Even though the US ended up dropping the charges and releasing Cienfuegos, the reaction in Mexico has been to pass a bill that makes it much harder for there to be any cooperation on drug enforcement, with Mexican police/authorities needing official permission to cooperate with any foreign enforcement officials, with US officials saying this will severely hinder any such cooperation in the future, a great present for the incoming Biden admin.
One theory is that AMLO has been afraid of Trump since his nasty tariff threat and was trying to keep on his good side, at least until the electoral college voted, even if he really did not foresee that Trump would fail in his efforts to overturn the election result. Another is that somehow he is stupid and actually thought Trump would succeed in overturning the election result. I doubt this, but in his first presidential election in 2006 when he narrowly lost to PAN's Calderon he contested the election result for a long time afterward, although without success.
I see two other reasons for this. One has to do with the renegotiation of the former NAFTA, which is now officially in place as USMCA. This may be tied to the negative of AMLO not wanting to anger Trump and have him impose new tariffs. Trump is proud of USMCA and, of course, denounced NAFTA as "the worst trade deal ever," although I think he said that about some others also. In any case, most observers see few differences between the two, most of them items that are in the TPP that Mexico (and also Canada) agreed to for being in that agreement, which they are, unlike the US. So no big deal agreeing to those items with the US, some of which amounted to modernizations. The only other item that affected Mexico could be viewed as a mixed bag for Mexico, Trump's demand on higher wages for Mexican autoworkers. This looks like a loss to the extent jobs are lost but a gain to the extent higher wages actually get paid to workers who do not lose their jobs.
The other item is something less admirable, and something AMLO may well share with both Trump and Bolsonaro, a certain egomaniacal tendency to authoritarianism. Even if it does not go that far, supposedly AMLO and Trump have hit it off personally. Indeed, AMLO actually visited Washington in September in the middle of the campaign, something he got criticized for in Mexico. I do not know what his personal relationship is with Biden, if any, but it is clear that he feels this personal connection, with it possibly boding ill for Mexico in the future if AMLO decides to pursue this authoritarian streak more fully.
The part that really is a bit mysterious, and has also brought criticism in Mexico, is what did he think he was doing in terms of relations with the incoming Biden administration? Most think that Putin has not helped himself with Biden by delaying recognizing the obvious, and we know that Bolsonaro is kind of a wacko as well as out there ideologically. But I would think that AMLO would want good relations with Biden, and I think he is smart enough to have known after the outcome was declared that indeed Biden had won and would be coming into office. Unless somehow he actually dislikes Biden personally, which I have not heard, the only way this delay makes sense is if he thinks somehow it gives him leverage by showing "independence," which is also coming with this new bill on cutting back drug enforcement cooperation, although I do not see how AMLO gains from such a lack of cooperation. Maybe he will gain this, but my own view is that I think AMLO has made an error here, and he is going to have to do some adjusting down the road, preferably sooner rather than later.