Bruh.
1. It wont be a peaceful event. Armed men with guns standing over every vote isnt peaceful.
2. It wont be democratic. Willing to bet less than 50% of the total voting population shows up. Also willing to bet the referendum will be weighted. Either with only options to join Russia, or the phrasing will be convoluted to ensure no one chooses the option to stay out. Something like "a. Peacefully join Russia, or b. Continue the violence against the aggressor Ukraine ensuring many of you die if you choose this option. Ignoring that many will still die if they join Russia.
3. By joining Russia those people will be forced to fight for Russia, and have their assets seized by Russia. That's not peaceful.
4. Annexation only comes after a peace treaty, pushing that annexation forward changes the game, hence escalation. It would be like calling a game in the early 3rd quarter after your team has gone flaccid and seen their lead shrink from 4 touchdowns to 1. They are trying to circumvent an ending they see coming/very possible that osnt favorable to them.
5. These same type of votes are exactly how this mess started. In Ukraines eyes this is opening a new phase of the war, so again escalation.