And not just dumb fun sells. 2015's Jurassic World was a really fun movie that, much like The Force Awakens, set the franchise up for a potentially great trilogy. These movies are only dumb fun because that's what Universal has turned them into. Nothing is every going to be as good as the original JP, but there was a chance for a really solid trilogy here and much like the first trilogy, after the first movie, it just turned into complete and utter nonsense.
The second a franchise devolves into "dumb fun" and that wasn't what the original intention behind a franchise, I stop watching, because ironically, that's when it stops being fun for me as a movie goer. It means that they strayed from their original vision and somewhere along the line got lazy either in the films direction, writing, etc.
Despicable Me (the original) is a movie that was made with incredible heart and a great start for Illumination. Then DM 2, 3 and Minions happened. DM 2 was where the downhill plunge started there. Less focus on heart, more on zany minions. Then a Minions film, which is just when I stopped. DM had a chance to be their animated Toy Story and have great film after great film, but they were more focused on selling minion plush than on the script after the first movie.