Meh, they have crimea already, but donetsk have coal and heavy industry. Anyway that’s irrelevant, because the point is to freeze nato joining via autonomy rights or frozen conflict a la transnistria.
I mean yeah, but the reason they want Ukraine to not join NATO is to 1. be a buffer 2. if Ukraine joins NATO they are obliged by design to send their troops there to take back Crimea and Donbass since the reason NATO was formed is to assure its members territorial integrity. So the main reason is still that they don’t want to let go of the virtually annexed territories.