This is a good point Zach.

Baku and the Kremlin do of course have cordial relations — with the latter supplying much of the arms to the former.

Russia’s interest in the region could be linked to three points:

1. Armenians and Russians are both majority orthodox, giving them a desire to support them
2. By moving against Azerbaijan, the hinder the rise of pan-Turkic sentiment and movements; potentially keeping the Azeris dependent on Moscow
3. Forces Turkey, with whom they have a complicated relationship with, to be knocked further off balance

Note: Russia need not intervene directly but could rely on the Wagner group.

Regarding Iran — about 17% of the country is ethnically Azeri. There have been a variety of protests across the Azeri-majority regions of Iran in support of Baku.

While Tehran might not wish to intervene, their hand may well be forced by popular sentiment.