So they amend their constitution. During a war. To force people into the streets to vote.

How does the government make sure the election is fair? Some people won't be able to vote due to danger. Some will be attacked. Some areas are occupied, and the occupation lines may change during the election.

If they tried to run an election now, Russia would publish their own results showing that the occupied areas voted for Putin. Trying to run elections is hard enough in normal times, doing so with Russia literally holding a large swath of your country is impossible.