What was the design choice behind going with abbreviated URIs for topics (/t), and categories (/c), but using the full form for accessing user pages (/users)?
Because /users is a page on its own whereas /t and /c aren’t 
5 Curtiram
The average end user isn’t aware of that though, just seems inconsistent.
The average end user isn’t looking at the location bar.
12 Curtiram
Shorter URLs, less desire to “localize” URLs since they are not full words.
3 Curtiram
Probably also because users don’t create super long URLs while topics do. I’m glad to have a convention that keeps these a bit shorter.
2 Curtiram
We need /u/ for /users/ 
6 Curtiram
Este é agora o caso e está implementado como /u/
7 Curtiram
Posso afirmar com confiança que nenhum dos meus usuários está prestando atenção nisso, lol.
4 Curtiram