Yep, it's totally possible to forget lucids if your recall is low enough. They may be more "memorable", but "memorable" is no match compared to low recall; your recall can either zap your recollection of LDs or improve it.

I would never have remembered a couple of my LDs if it wasn't for a trigger or seeing a certain topic during the day. In two of these instances I remembered an LD when watching a movie or something... Late at night, almost when I was about to go to bed. If I hadn't watched those movies, I'd never have recalled that lucid and it would've gone completely away.

I'm sure there's a few that I've totally missed; a few nights ago for instance - I woke up feeling like I had a lucid, but my recall is poor at the moment... So, no recollection or anything, even now.