Everyone has their very own personal notion of "how it should be".
For instance, I don't think I should lose the part after defecting the power. It doesn't belong to them - I put in the time, I jumped through the hoops, and I bought it.
It wasn't given to me as a perk.
I'm totally OK with losing the ability to purchase a new one after I defect, but I shouldn't lose what I already bought (as long as I can cover the insurance).
Such a change would only make PP modules even more unappealing than they already are.
PP is frustrating enough as is, so you might as well just get rid of it, instead of reducing it to complete pointlessness and watching as it dies a slow, agonizing death.
Selling and rebuying modules was the only option to transfer equipment between ships, and it worked reliably, until suddenly it didn't anymore.
The fact is that those people never had the intention to part with their modules. They were using the only option available in the game.
And that is very frustrating, because the inability to keep AFTERMARKET modules that you bought SEPARATEDLY from the hull doesn't make sense at all.
I mean, currently if you want to trade in your ship, first you have to sell all your valuable modules, then you sell the hull at a loss, then you buy a new, different hull and go on yet another wild goose chase to find the modules you want for your new ship.
If by chance one of your old modules is a fit, then the option to rebuy it will save you that much time - it's a clunky mechanism, but it worked.
Chasing for parts might sound awesome when you're finally trading your sidey for your first cobra, but after a couple months it gets really, really tiresome.
Besides, removing the ability to swap equipment from one ship to another will not prevent people from collecting different PP modules. It will only make it more expensive and burdensome, and it will affect only the players who don't have enough money to buy several different ships and fit every one of them as the modules become available.