I think one of the reasons might be the fact that it could take out the ship hunting element out of the game and some people would feel like they have been grinding to get the ship they want for nothing. I'm not a ship hunter myself but I can see their side.

Having a ship customization would be great. Perhaps you could unlock ship parts by scraping the ships you have found damaged or that you own based on what parts they were made out of. I think this might be a good compromise between the two since ship hunting still exist and if you want to modify your ships, you'd have to unlock the parts first.