There was once intended to be a second, older Moonrise Tower in Baldur's Gate 3 that you'd also explore, but "the game was getting too big, and so we had to cut that out."
I think the pacing is just off once you get close to the end.
Once you get to Baldur's Gate, the game is a slog. If I didn't want to get the golden dice just so I could say that I got them, I probably wouldn't've finished the game.
100 hours is too much for a game. Let's say I can play it 1-2 hours a day 5 days a week (I usually have stuff to do on the weekend), it'd take me over two months to finish it! There are other games I want to play!
I did finish it, but only because I had to spend over a month at home using up PTO before leaving my previous job for my current one.
Seriously, a typical D&D session might last 6 hours and you accomplish nothing of note, but you have fun! Enjoyment should not be transactional with time.