Episodic memory is not really learned, is it? There's a semantically confusing syllogism in there. If a memory is pondered often enough, there might not be much more to learn from, thus you stop thinking about it and as with muscles, it deteriorates if not used. But what you have deduced from that memory might have value. Eventually you might learn later on that episodic memory is a valuable thing to keep as much as possible, thus we reminisce. On the other hand, maybe early childhood is just so terrible that it needs to be suppressed.

Even if you aren't able to recall useless events in your life, you still have memories of most of them with the appropriate cues. Tgat doesn't hold for early childhood.