There are a few assumptions you have to accept to understand why low end plastic is used.
1. All discs beat in. If someone made a truly indestructable plastic it would be a major scientific breakthrough.
2. If you look at the way a disc beats in, it will beat sorta quickly at first and then slow way down so that it doesn't change flight much for a long time. After that it gets gradually more understable at a fairly slow rate.
3. If you observe how discs in high end plastic beat compared to how discs in low end plastic beat you'll find that the high end discs tend to loose HSS faster than LSS. The low end discs will loose LSS faster than HSS.
4. In general, and this applies even more to discs that come recommended in low end plastics, you'll find that the high end discs start off more overstable, meaning you have to pick a more understable mold to get a good flight when new.
5. Not all low end discs beat in fast. Some do, the ones I'm talking about (putters, stable mids, stable fairway/control drivers) don't. The wear is gradual.
What all that means is that if you pick a disc in a high end plastic you'll have to pick on that's either too overstable to be controlled well and then wait for it to get beat up (which most people agree it takes a decent amount time to beat high end discs), or one that flies well when new and have it get squirrley when it does beat in (which will generally happen faster with discs that don't start off overstable). That makes replacing a beat version of the first type I mentioned extremely difficult and replacing a beat version of the latter necessary no matter whether you lose it or not.
It also means that the beat versions won't fly nearly as well as beat versions of low end discs. Losing HSS means that discs tend to get squirrley easier and it makes anhyzers and turnovers more diffcult because the disc still wants to fade out. Losing LSS means straighter flights with the disc still being controlable because the HSS is predictable.
Also, how many threads are there about the flight differences between colors and runs of high end discs? How many are there about the flight differences between colors or runs of DX Teebirds or DX Rocs? There just seems to be less variation in runs of the lower end discs. That means that when buying a new one you'll have a lot better chance of the disc flying how you expect without having to find a certain run.
Cycling discs isn't as hard to manage as you'd think. As long as you keep a backup or two of the discs in the best stages of wear there won't be a shot you can't perform. Plus, getting discs to that stage means you'll know the disc really well by the time it gets to that point.