He’s famously flexible based on whatever he thinks is advantageous now. This could be as simple as his claims to have been unfairly persecuted by law enforcement, it could be part of his wealth gained from cryptocurrency, or it could simply be that he thinks it’ll make his opponents angry. Rich people often act on whims just to show that they have the power not to need to justify their actions.

AFAIK, it wasn't done because he wants to be lenient on drug traffickers, but because the overall case of Ross Ulbricht is huge in certain political circles that he was pandering to during the presidential race, so seems he's "paying back" for those votes or something.

There is a high correlation between his condemnation of drugs and characterizations of families, many poor and desperate, illegally crossing the border.

Most illegal drugs by far go through regular border crossings, but he hasn’t obsessed about them in the same way.

Basically he did it to get the vote of the right-libertarians. He made a promise to them.

They idolize Ross for creating a drug market because they view it as freedom of speech.

Trump has never been a big drug warrior (against drug users). His social views are basically late 80's 1990s Democrat and not out of line with Clinton, etc.

It was a big cause that many libertarians cared about. I'm sure all the crypto people who have Trump's ear have been pushing him on this. There are also rumors that some state-level libertarian leaders promised not to promote their candidate if Trump promised to free Ulbrecht.

Trump is predictable. This was his side of a transaction designed to secure support from a voter contingent. His personal opinions don't matter much when he is making a deal.

Crypto commodity grifter gets known crypto commodity laundering expert out of jail.