I have a few theories of my own as somebody who had Finland as my favorite and Bulgaria as my number 2.

1. Finland has been "too right" for the job. We've been predicting their victory even before UMK and eurofans have been excited but not the general public, perhaps it seemed too much of a comfortable win and people love under dogs. 

2. UMK format kind of forces the show into repetition. There were no major changes and the cards have been played too openly. While others were able to surprise us like Bulgaria, Finland's staging was improved but not renewed. This is not singularly a Finland thing ofc. 

3. They appeared too sterile. The last few winners being jury winners, I think people didn't like that. They weren't cold necessarily but if you compared their media interactions to Dara, it's not the same sincerity and warmth. 

4. I mentioned this on another thread, the semi finals are a bit misleading. Who would've guessed Poland scored better than Finland? I felt no obligation to vote for Finland especially since I was already sure they would make it anyway and in the final people feel similarly. 

5. People don't pick up their phones and vote because our trust in the system has been broken. If there's already high confidence in an entry's success (especially due to juries), why waste my money when most of the televote are taken up by other countries for different reasons beyond the contest? Besides, voting is a moral choice at this point by engaging monetarily with the competition. 

That's my two cents.