It isn’t pride, Russia needs Crimea in a way they really don’t need the Donbas. The Donbas was once an industrial hub, now it is just a shattered wasteland that will be an economic millstone around Russia’s (or Ukraine’s) neck for decades, regardless of its coal and iron deposits. Crimea is a strategic prize, home of the Black Sea fleet even after Ukrainian independence. They were to be under lease initially until 2017, then extended to 2042 (with option for a five renewal afterwards) by a pro-Russian regime in 2010. Russia of course made that moot by seizing Crimea in 2014.
Russia has made Crimea very difficult for Ukraine to take by force by building elaborate defensive lines starting in late 2022 in reaction to the successful Ukrainian counter-attacks against Kherson and in the Kharkiv oblast. This switch to mobile defense in depth is the main reason the attempted Ukrainian counter-offensive in 2023 stalled out. Putting pressure on Crimea by effective blockade is an entirely different tactic, but Russia can’t really afford to blink on this one.