Even if taiwans technology manufacturing gets destroyed in the invasion, it’s still major part of western world’s component infrastructure. They can also just rebuild. China gaining control over that or even just denying it to west would make china internationally more powerful no matter how it goes.
Most likely that isnt the only reason they want taiwan, but i dont believe it isnt one of them.
even though there are enough signatures now, they still need more to be sure. Some percentage of the signatures will be invalid(people unable to spell their own names and fakes for example) so there has to be big enough safetymargin. Ross made video about it too.
So until the time runs out, everyone should make sure the safetymargin is as big as possible.