I was just going through the accounts section of the help page when I noticed that bit. 5th bullet point listing the benifits of privileged accounts.

Why do only trusted users get access to an upgraded searching system?
More importantly, why is it that the tag limit for 99.99% of users lower than what it could be?

more tags in the tag search cause more load on server. allowing everyone to use more tags in searching could cause servers to slow down a lot. privileged users get to use more tags in searching because it can be very useful for tag projects and helping with site in general

I guess you can say that they are... privileged

But seriously, good users earn good perks.

Longer tag searches are more taxing on the server, and the limit is raised for higher accounts to give them another useful tool.

We also trust them enough to use that power responsibly.