Why? Russia lived without the Crimea from 1991 until 2014.
From 91 until the 2014 coup, they didn’t care because their navy base went on as normal. But with the ethnic cleaning in the Donbass sure to happen if Ukraine could get into Crimea (they can’t) the Russians won’t let it go.
And despite the fantasies of DC, Crimea will never become a NATO navy base. It’s been a Russian navy base since the 1780s, they fought the Crimean war there, they fought a dreadful battle there against the German nazis... they won’t be letting it go.
It had Sevastopol by lease.
Ukraine and Russia were still mostly buddies during that period and Russia felt no need to upset the status quo. Things obviously changed after the 2014 coup.
You're completely ignorant. The Russians have operated a naval base in Crimea since the last 1700s including during the period of time you reference.
Russia had full use of the naval base at Sevastopol during this entire time and had signed treaties with Ukraine guaranteeing use by the Russian navy until 2042.
In exchange, Russia provided Ukraine with natural gas.