Pool builds outlast the tools meant for a one-day service call
Rented software is mostly designed for short jobs, and a pool build runs for weeks with hand-off after hand-off.
The daily problems are specific: confirming the next subcontractor, knowing which inspection a job is waiting on, making sure the steel passed before the shell crew arrives, and arranging backyard access for equipment and spoil haul-off.
Homeowners add their own layer. They picked upgrades in the design meeting, they want to change the tile partway through, and they call when the yard has looked the same for a few days.
A generic project tool can hold a task list. It does not know that a shell waits on an inspection, or that a payment comes due when a stage is done.