On ServerFault, we have 3 types of questions that are banned (each of them has a custom close reason), they each have a different history and background.
The first two types have been banned for a long time so they don't really fit the "originally on topic" aspect of the question, but there was a time early on when they were on topic and there was substantial discussion about whether to ban them.
Questions should demonstrate reasonable information technology
management practices. Questions that relate to unsupported hardware or
software platforms or unmaintained environments may not be suitable
for Server Fault.
This one covers (mainly) questions about out-of-date platforms and technologies. Questions about NT Server 4, support for Windows XP, using a Rasberry Pi as a web server, etc.
Questions on Server Fault must be about managing information
technology systems in a business environment. Home and end-user
computing questions may be asked on Super User, and questions about
development, testing and development tools may be asked on Stack
This one is pretty straightforward. Questions about consumer-grade equipment are off-topic, even if used in business.
For both of these, when the custom close reasons were first set up, there was a good consensus to get rid of them, and whenever the close reasons were updated to make them clearer, there was still broad support for leaving them off-topic. Because the close reason was revisited and improved a few times, it's a nice, short explanation and generally satisfies anyone who asks "why isn't this on topic?"
Unfortunately, the improved/nicer closed post notices that were implemented recently hide the close reason from anyone whose rep is too low to vote to close, which leads to confusion:
The other type of question that's off topic is control panels:
Questions involving web hosting control panels are off-topic because
they customize their systems so that standard system administration
methods no longer apply. Some related topics may be asked on
Webmasters or see Where can I ask questions about web hosting control
At the time this was implemented, cPanel and other control panel questions were a plague on the site: there were lots of them, they were usually unclear, often went unanswered. There was almost unanimous support for getting rid of them.
The only controversy with this was that a moderator election was held shortly after this was implemented and one of the new mods took it on himself to get rid of tons of these. This was widely supported by the community (doing so was part of his election platform), but the way he did it bothered a staff member, and then the staff member's response pissed off most of the community.