I'd say...
...a fair few PPLs read pprune. Some with professional aspirations, some not, but perhaps the binding thing is that they want to be in and around people who've gone the distance. A mark of respect, so why wall off the wannabees/couldabeens?
...PPL is the single biggest identifier with amatuer pilots. Yes, it's light aviation, and yes, a few months down the line you'll pick up on the GA acronym and have your own definition (as demonstrated in this debate) of what that might be, but there is one single bunch of letters that's the starting point for pilots - PPL. So, if pprune sees itself covering that starting point, then why not a PPL forum?
...and whilst there isn't? PPLs and prospectives will be trading 'Which US School' type questions in a random-ish forum of their choosing. Right now I'm getting superb and detailed advice about the very same, as a result of replying to postings that sit alongside vociferous debate about the merits of landing their employers' jets at LCY.
Just my 3-4k's worth.
So, amyway, flying schools. I've heard really bad things about... ;-)