My take on the current situation as someone who's watched the conflict since 2014 (both professionally and casually):

Russia's nuclear weapons arsenal is serving its intended purpose right now: Scaring Westerners. If you listen to Putin's speeches, he's been remarkably consistent. He cares about Russia's place in the world, addressing how it's not treated as an equal partner (by his and other Russians' measure), the desire for a multipolar world, and general nationalistic sentiments.

Nuclear threats raise the ambient level of seriousness with which the general Western public, and by extension its governments, must take Russia. Getting that benefit only costs vocalizing the occasional reminder. So, from a game theoretic perspective, it makes sense to do so. Those purposes aren't served by actually using nuclear weapons.