You ask a question that require a 2 part answer.
1st Why pick a Generic when there's an In house movement available?
There are several reasons I will only focus on movement side of things
1. In house doesn't make it better. Season watchmaker will tell you new doesn't always mean better. New things always have tiny problems to sort out because it is new.
2. Some of the most reliable movement comes from movement supplier, ETA, Lemania, Valjoux ... etc. A beautiful movement is one thing but the most important thing is to make it work continously.
3. The Lemania movement have exist for many years. It is been tested and use by a lot of manufacturer and a lot of refinement have been done.
4. Historically PP is not a movement manufactuterer but Lemania is. A 80+ years movement manufacturer and a luxury watch assembler which one will you trust?
5. A movement that's been widely use by others doen't mean is inferior just not exclusive.
2nd People prefer what they have bought themselves
1. Wouldn't you? It only make sense since that the reason we buy watches.
2. "newer pieces are conceptually purer and simply more bespoke" Doesn't this statement tell us that the most important focus here is exclusivity which can not warrant a fair discussion.
3. Bespoke in watch will be going to an independent and build a piece unique. Owning a PP will give a us prestigious feeling, but bespoke?
4. If exclusivity is what we're looking for I think Lemania-Based PP will be a safe bet. There's no way of telling how many new in house movement watches PP will produce. I am almost 100% it will be more than the Lemania models.
Finally,
PP, VC, and AP have their history written in refining and assemble parts from 3rd party into their own brand. It's a dying art since most people these would prefer an inhouse movement. There is something romantic and satisfying of seeing a master watchmaker turn a ordinary movement into a masterpiece. People who in the knows greatly appreciate there are only a few.
Inhouse movement have turn itself into a marketing tools nowadays. It use to be purely for a better product but now we seems to be getting further from that. I'm accusing PP I'm just saying what I saw and some inhouse PP are great.
Hope one day you can find the joy of appreciating a finely rework generic movement in a fantastic watch.
Best
Tyler