Care to say why?  No...
oh well.  it's not terrible anyway.  Far from it in fact.
Reasoning:

True Johnson's vanishing act in certain episodes is not handled that well, but he's still in most of them and in some he's the main character by far.

The season doesn't have the bad comedy episodes, it's straight ahead serious with some solid, tough and rich stories.

The action also has more bite (some of the earlier action in "Vice" is very bad, with people who can't fire guns and people being shot but falling down like they suddenly went to sleep) and there is far less of that (getting very silly) bright pink and green lights shining on every single room and building.

Tubbs' outfits were bad at times that's for sure, but lets not forget that season 5 is really a 90's beast not an 80's one. This is shown in Crockett's wardrobe.

I can understand why Season 4 (though it had some good episodes) gets a bad rap but i truly do not know why season 5 does.
Hell even the non-Jan Hammer score sounds like Jan Hammer.

It also has a pretty damn great finale double-header.  A powerful way to end the series for any "Vice" fan and punchy with it.
My only problem with the finale was that there was no real goodbyes for the rest of team and that I wish it had not been a new bad guy but a return for 'the one that got away' G.Gordon Liddy.
Other than that, a solid, good, much improved from the last one, season with a great ending.