You are confusing the initial construction with the long-term ownership. Most of the time, the corporation that builds the apartment block will sell the apartments, not continue to own them and rent them out.
The developer and property owner are (usually) still different people in this case. Owning and constructing a rental property have very different risk profiles so the same people don't want to be in that business.
> The developer and property owner are (usually) still different people in this case.
I would say the general contractor might be different, but the developer and property owner and always the same where I live for tall apartment blocks with 100% rentals.
Even if this is true, this is a distinction without a difference. If a developer can't sell their property to someone else, there's a good chance they wouldn't build it in the first place. If they do decide to never sell their apartment complex, they won't have the liquidity required to build another.