Yeah, Alafia is popular with the snowbirds. Might have something to do with it being $22/night.
If the LAL loop is full, it is okay to book a site in LLL (horse loop). We prefer staying there and always hope there will be horses "camping" with us.
I called Alafia this afternoon and according to Ranger Brian (a new guy), it's still okay to stay there even if you don't bring a horse. (RA web site has a different opinion and doesn't make it easy to book on the horse loop). Just a FYI.
Also, Ranger Brian didn't know about any RA glitch causing empty sites to show as reserved. The RA web site shows good availability for most dates 'til snowbird season.
I wonder why the OP wasn't able to book there.