I have a hard time believing that GOG rejected a Zachtronics game. They're popular, high quality, and a good match for the GOG audience. An GOG already sells several of them (I own SHENZHEN I/O and Spacechem on GOG).
The rejection of Opus Magnum got a lot of attention at the time, which probably caused GOG to reconsider. But most developers don't get that kind of attention, if a game of theirs is rejected. I've seen multiple developers of games that I like, saying that they've given up on GOG because of the curation