Nobody really exercises ‘for the sake of it’ though, do they?
Everybody gets something out of it, whether it be increase in fitness/weight loss/enjoyment/ whatever. Even the people doing it for vanity, ‘to get the perfect body’ have an aim in mind, are working towards an end.
OP, you need to realise you don’t want to exercise for exercise’s sake, just that your aim isn’t enjoyment any more.