They did, but when it came to the annexation topic to rejoin Russia that he supported. The majority of the people in Ukraine stood up against him which is their right in a democracy, and ousted him. Only the ones in Crimea and a few others supported him, but the majority did not. The government that is now in place with the support of the majority of citizens in Ukraine do not want the annexation and therefore want there governmental buildings back.
Even though the U.S. and united nations have conceded Crimea, Ukraine has not !!!
What about Russia's nuclear fleet? controlled by the chain-of-command among street protesters?
The US would never agree to such a situation with its own nuclear fleet.