Oh, I definitely know it made a lot of people unhappy! It's the #1 complaint people made about the game, and if I'd known that coming in, I would have done things differently - put more work into the plot to justify it, rearranged the levels to keep parts being introduced more consistently, just had more superfluous parts included in levels...
It's something I've taken into account in my next game (Manufactoria 2022), for sure. I do want people to enjoy my games! This frustration just wasn't something I ever anticipated or saw in playtesters.