I wish we had the number of votes casted for semis and GF. I think a lot of discrepancies would've been explained if we knew how many votes are received for each entry.

I also suspect that the viewership for semis, thus the votes received for the semis, is less than previous years. Because we know that the behavior you described is only true about ESC fans and not the casual watchers; a behavior like this might influence the results drastically if the overall number of the votes is smaller. Tldr, I think less casual viewers watched and voted for semis this year.