I think it's less about laziness and more about keeping production costs low. Those that want a different cage will buy a custom one or modify the stock one. Most will leave it as is.
Requiring a fitment for each driver would add a LOT of expense in the form of manufacturing and stocking different sized/shaped cages, a lot of paperwork, dealers keeping extra cages on hand, etc.
If they didn't stock them and the right sized cage had to be ordered, a lot of impulse walk-in sales would be lost.
It's just not feasible to do a custom fit for each driver.