Hey,
I wouldn’t get caught up with hard rejects. In many ways i agree with what @SergeBales said; don’t delete tracks however, keep them to compare what wasn’t approved for the market with a track that was approved. Many times in the moment its rejected, we think to ourselves how though? but then some time later when we have some tracks approved, we go back and listen to these rejected tracks and realize that the track might not be bad at all but it doesn’t appeal commercially or there’s a small mixing issue or maybe the arrangment in the song somewhere is weird. There is lots to learn and we continue to learn as musicians. Never will a musician reach a certain skill level and then from that point just be at a constant flow with nothing more to learn.
Sure, you can upload your rejected items to other marketplaces and sell them there if you want to, but if you like to focus your efforts on one marketplace, try to have the mentality that it wasn’t approved for the market and thats OK, focus on your next track and you will constantly improve.
Good luck! 