That did occur, but two points. First, any additional avenue for censorship is bad. Second, it's a completely different mechanism. There, if I recall right, web hosting companies refused to host the website. Worth noting, this can be routed around by hosting the website in other countries or even on one's own computers. Still I agree it's a form of corporate censorship.
However, the corporate censorship opened up by removing NN is much more direct and, I argue, frightening, because there are much fewer ISPs, and they can directly block users from accessing the site very easily. Once they start it will be very easy for them to grow their blacklists quickly. Further, it's actually in the direct business interest of these ISPs to block sites in many cases, which was not the case for web hosting. Finally, it's much easier for governments to step in and start censoring via this mechanism since they can control all ISPs in their own country -- not true for web hosting.
However, the corporate censorship opened up by removing NN is much more direct and, I argue, frightening, because there are much fewer ISPs, and they can directly block users from accessing the site very easily. Once they start it will be very easy for them to grow their blacklists quickly. Further, it's actually in the direct business interest of these ISPs to block sites in many cases, which was not the case for web hosting. Finally, it's much easier for governments to step in and start censoring via this mechanism since they can control all ISPs in their own country -- not true for web hosting.