Why are unregistered users not allowed to post questions on some sites?

Question

I know this isn't a big deal for me but why do guests get to post answers but not post questions?

Answer 1

This restriction isn't network wide and applies only to Stack Overflow and some other Stack Exchange sites; see a list below. You don't have to register to ask questions on most other sites in the network.

The change was made because Stack Overflow has grown in popularity and the number of hit-n-run questions by unregistered users was getting out of hand. It's a quality control measure.

See Encouraging users to create an account (and keep it) as well, specifically Jeff's follow-up comment:

@eds it still works, just not at the scale of Stack Overflow. And to be brutally honest, the important part is unregistered answers; we don't really care about putting barriers in front of question askers. See https://blog.stackoverflow.com/2011/06/optimizing-for-pearls-not-sand

The complete list of sites requiring a login to ask a question is:

• Arqade*
• Ask Ubuntu
• Blender*
• Christianity*
• Database Administrators
• Electrical Engineering
• English Language & Usage*
• Mathematics*
• MathOverflow*
• Matter Modeling*
• Meta Stack Exchange*
• Motor Vehicle Maintenance & Repair*
• Movies & TV*
• Physics
• Politics*
• Software Engineering
• Stack Apps*
• Stack Overflow
• Stack Overflow in Portuguese*
• The Workplace*
• Travel*
• Worldbuilding
• All per-site metas (including those that allow <5 reputation users to participate)*

* Sites with this symbol also require registration to answer questions.

The links above are to documentation (either a meta post or a chat message) as to why the requirement was enabled on each site.