I think that initially it was not as obvious that colin Trevorrow’s script was problematic till Carrie fisher died. Remember that Carrie fisher was suppose to play a larger and larger role as the trilogy went on. Without Carrie fisher than colin Trevorrow was left with no story core and it became obvious that she and her brother were meant to be the emotional cruch of a script that was obivously not very good without those elements. So kennedy fired him when it became obvious
Remember that colin was never truly the writer of jurassic world…most of its story problems came from the previous planet of the apes writers