Question: why do courts hit DNS providers instead of domain registrars?
Most of the eggs are in one basket. Same as trying to get individual ISP's to censor something, reaching out to each of the hundreds of registrars is time consuming and prone to being ignored depending on the country. If on the other hand a government can get cooperation from even 3 of the biggest "free" resolvers then its a big win for them. It's also easier to monitor people when they choose to use corporate resolvers like Cloudflare, Google, OpenDNS, etc...
Most of the eggs are in one basket. Same as trying to get individual ISP's to censor something, reaching out to each of the hundreds of registrars is time consuming and prone to being ignored depending on the country. If on the other hand a government can get cooperation from even 3 of the biggest "free" resolvers then its a big win for them. It's also easier to monitor people when they choose to use corporate resolvers like Cloudflare, Google, OpenDNS, etc...