Because countries(especially ones which struggle with poverty, constant terrorist attacks, constant fighting with multiple hostile nations bordering it, and a billion+ mouths to feed) can't change their entire foreign policy in a single day just to virtue signal to look good to the west. Especially when the west has historically always turned a blind eye to India's troubles in the past, or worse, actively supported India's enemies. Pakistan, Srilanka, Bangladesh also abstained btw, and tbh it's kind of understandable given that they also have their own issues to deal with.

Also, it is untrue that India don't give a shit about Ukraine. They've been sending aid.