I'm not sure what you mean when you say that developers serve no purpose. Maybe there is a definitional problem here. Maybe you are thinking of planners rather than developers. Developers organize, design, finance, and gain approvals for housing projects. Often they are also the general contractor for the building phase. Planners, on the other hand, ensure that projects meet the requirements of municipal Official Plans and the Planning Act (in Ontario).

It is true, though, that a lot of developers submit shitty plans that municipal planners have to fix. That's because the average developer doesn't give a single shit about the public good and only seeks to maximize personal profit. So, they treat the Planning Act as an obstacle to work around rather than making a good faith effort to follow the principles of good city planning.