I can see why you think this, but it doesn't make sense within the game. The idea is that each time you start again, you're doing so from scratch. There is already a concession to 'XP' in that you can unlock different ship layouts and also earn achievements - have you looked at those yet?
I've been enjoying the 7 or so games I've played of this, but I'm starting to get annoyed by my feeling of lack of progress.
It would be nice if playing a game set you up better for the next time you play. Maybe things levelled up, etc.
But the notion that you're not progressing is supposed to be dispelled by the fact that every time you start over you try to get further. You should be noticing that you're learning tactics, strategies, which power-ups to keep, which to ditch, when to cut and run, when to stand and fight, and how best to prepare your ship for the final stages, before you get there.
Also, you're meant to die. A lot. This is so that you start over with new lessons learned. And then die again, a different way, so that you start over with yet more new lessons learned.
That's the design of the game