Most developers would not accept those terms. That's a proposal for predictable project losses. It's far less risk to own the project and land, seek institutional and similarly deep pocketed financing, then to suffer the fickle stinginess of a multitude of strata members. The developers who accept those terms will be looking to cut corners.
There are plenty of projects that are sold before they are started, and no reason the transaction would have to go the way you're claiming.
As long as at least one person is willing to assign their land claim to the project it could continue without that portion taxed, and acquiring or renting the claims would not have to be coupled to funding.
Modelling land as a fungible commodity that you're allowed to have as much as you want of is stupid and is just gifting a large portion of the productive output of society to those privileged enough to take on debt and those with the magic loan wand. There are plenty of other systems historically and currently that aren't as insane.
Pre-sales always include broad sweeping allowances for variances in final cost; for instance, folks who pre-bought condos two or three years ago are just starting to get sticker shock now that the final price has hit them, thanks to skyrocketing materials cost. The price they agreed to pay, with those variances they agreed to.
Without the assurance that someone else would shoulder the risk the builders would have walked away. Like they do in China, and where they have to demolish half finished towers because the builders dropped out and none will take it on.