That's one of the smaller reasons since the annexed regions are also considered "Russian borders" now (95% of them voted for Putin in the recent election in Russia).
Where did you get this from? Let me guess, official Russian media channels that reported almost everybody voted for Putin. The whole country is pro Putin. The problem is that you cannot and will not get any legit information from Russia. In one of the elections they had so many fake votes for Putin that the total sum of votes exceeded 100%

Yes, the majority voted for Putin. No, it wasn't even close to 80%, not to mention 95%. Things like that don't happen unless the election is tampered with, and Russian elections have been fixed for decades.