Still JPMC assumes that it will make them money. So it won’t help with housing affordability and availability.

You can both reduce unit price in comparison to the market and make tons of money. Happens all the time. The t-model is a prime example.

model-t didn't require a lot of zoning/permits/etc. at least, at that time.

How can it not help housing availability by increasing supply?

Traditional property developers don't usually hold onto the properties they build, they sell them off. Even skyscrapers sell off their apartments and commercial sections. Maybe some don't now, but I think that might reflect a shift from building being most profitable to renting being most profitable. In that case, eventually a renting-developer would lose incetive to build more as not to dilute their rental margins.

And the people buying them also have profit incentives. Whether JPM is doing it to profit from rentals directly or with the expectation that some future buyer won’t make a difference.

But it’s illogical by any standard economic model that any supplier will not build more units if they see it can bring in more money. Either they build more or someone else does.

Elon Musk. Jeff Bezos. Warren Buffet. Sam Bankman Fried until not long ago.

None of them did it using a sole proprietorship. They all set up corporations. What’s the difference?

They can sell their personal shares in their corporations to fund it.