Most give up flying, of course, having got the PPL, and not having the money, or not wanting to spend the money, is one factor.
Others switch to cheaper forms of flying (microlights, gliding, and stuff).
Others spend £2k - £3k per year renting a club aircraft once every two or three weeks (cue usual thread full of usual people ranting that "if you can't afford to fly at least twice a day you can't possibly be current enough to be safe so you should give up").
Others with lots of money buy their own aircraft and fly every day.