I have the right to spend my money on closed, proprietary hardware and software.
of course you can use proprietary drivers. it's just that they harm linux development model.
what do you think would happen if nvidia would try to enforce a certain api on the kernel, threatening that they will not adapt the driver, and the kernel should be fixed instead?
linux developers would have to choose - agree to nvidia, or ignore them and have them fix their driver; kernel is more important.
they would definitely do the latter, despite the angered users, left with broken drivers.
also - bug reports from using a kernel with proprietary driver are usually rejected immediately, because this kernel is referred to as 'tainted' by proprietary software. the problem might exists within the blob, which is not kernel devs responisibility.