Duh, now I get it.

Why don't our customers get incremental development? Because they work in a waterfall environment.

Some of their processes currently takes days to run. They will get all the numbers late in a month. And then they must report on the results of running the process by the end of the month. Missing a deadline is monetarily costly.

Checking and rechecking their setup and data makes sense because of the time cost of running the process. Upfront work and preparation in their business is cheaper.

Unfortunately, it isn't in ours.