Your not the only one who noticed this. I don’t really have a good answer for this, but if I had an answer, it’s probably to say it has to do with budget.
Around between 2005 and 2007, they were working at 2 things at the same time, so they probably wanted to save money to make most of the money go towards the 13th movie, but less of the money decreases as Universal creates a new episode.
Then as they decrease the budget for the TV series, and increase the budget for the 13th movie, I believe that’s how the garbage animation came along after the first episode.
It’s not really that clear, but I hope the theory I thought of helped solve your question.