I'll repeat myself like I have each time I see this sort of thing mentioned. Timeshares aren't an investment, they're an analogue to Sam's Club for vacations, except with an initial buy in. The MFs are the yearly membership fee.
I see many claim you can just rent for similar to MFs, and that may be true, but those aren't the places I choose to own. I just got back from Vegas on the strip at Flamingo 2BR - there were no rentals offered for a week at that time, and I calculated it at $167 a night, which none of the shorter rentals came close to. Here we can discuss like for like issues - I didn't see any other timeshares that were on the strip at a casino than Elara, also HGVC and more expensive. I know the Marriott that was next to a casino there wouldn't rent cheaper. The cheaper options I considered, but the person I was taking did not want to stay off the strip, even a block. So that let out some of the great deals on Wyndhams etc. Even HGVC Boulevard was too far north from the casinos for what my mom wanted.
Even for off the strip, the RCI deals in Vegas are better than vacation rentals I've seen, many are available Last Calls for under $500 for 2BR for a week. Maybe you have a better "in" but I don't know of one and I semi regularly look to "prove the TUG wisdom 'right' and myself wrong". Orlando is the same way. More surprisingly to me is the deals at Smuggs in VT, Massanutten and Williamsburg in VA, Branson MO, etc. Other areas of FL when I've looked, like near Cape Canaveral etc still don't seem to swing vacation rentals way.
More in-demand locations still compare pretty well. I think I just found the first time where the AirB&B would save over the MFs and that's in New Orleans vs the Wyndham La Belle Masion, which coincidentally is the most expensive points reservation I've made yet. And that's still taking on the greater risk IMO of AirB&B that I'm not sure I want to ever do.
The main limitation is of course the locations. However, many of the locations are places I want to go, or places I'd never have considered without timeshares.
Hotels are so expensive and cramped that if I can avoid them I generally want too. Especially once you need 2 rooms.
I think the reason timeshares don't appreciate is still entirely the developers / retail sales being stupendously over priced, yet still very effective. I bet if everyone was buying at resale prices, there would be a lot less people getting "talked into" something they can't afford and probably less people trying to dump them. If you've got an additional $30k in your pocket up front, you've got more cash for MFs IMO.
That said, there will still always be people who are done with a timeshare and just want to pass it on. I guess if the retail sales were different and it was both easier to sell on a timeshare and the resales kept the benefits of the ownership we'd see more people buying with the MFs in mind and buying more like Sams Club memberships - the people who are going to use it and realize savings, and so not have masses wanting to get out in any possible way.