So the clearance is needed for the footrests found on wheelchairs, and if you make the stall big enough, you don't have to provide the floor gaps. It's interesting that the ADA regulations have become an important factor in design starting in the 1990s, yet I remember that public restrooms have had those floor gaps since much earlier than that. I wonder if the logic went like this: floor gaps have existed since at least the 1960s --> people with wheelchairs found the gaps useful to maneuver in the restroom --> the ADA codified this into a regulation in the 1990s.

To save everyone from having to wade through stack exchange, here is the ultimate link[1]:

"604.8.1.4 Toe Clearance

The front partition and at least one side partition shall provide a toe clearance of 9 inches (230 mm) minimum above the finish floor and 6 inches (150 mm) deep minimum beyond the compartment-side face of the partition, exclusive of partition support members.

EXCEPTION: Toe clearance at the front partition is not required in a compartment greater than 62 inches (1575 mm) deep with a wall-hung water closet or 65 inches (1650 mm) deep with a floor-mounted water closet."

[1] https://up.codes/viewer/ada/chapter/6/plumbing-elements-and-...