Applying for a single Dorm

Hey so I just finished my Housing application and went in thinking I was going to be able to choose specifically that I wanted a Single and at the dorm building of my choice but when I was applying it asked for at least 2 preferences and one of the options was “any single dorm on campus” so I chose that and as my second preference I chose a double and at the dorm building that I wanted but what I’m curious about is why wasn’t there an option for a single at the dorm building I wanted? Is this because perhaps many people have applied for a single at the same building I wanted? Or that’s just how the housing applications are?
Also there weren’t any options for a single at any specific dorm building" the only option for a single was “any single on campus”
I’m just curious if that’s how the housing application is or if it’s due to many people applying for singles. Thanks for answering!

Which school? Are you an in-coming Freshman or transfer?
Single rooms are rare at the UC’s especially for Freshman.