well i've indeed considered a4988 and drv8825, just that a4988 and drv8825 runs on the step and dir pin protocols, this requires the mcu to run in a tight control loop to time each (micro) step and when there are multiple steppers the mcu would be pretty busy simply running the steppers and having little timeslice for any thing else.
in addition, the a4988 and drv8825 modules (drv8825 being better) has small chip surfaces which makes them very hard to cool
one other disadvantage is a4988 and drv8825 uses the step and dir pin protocols and these pins can't be shared, this very much limits the use on mcus / boards with few pins.
hence the motivation to use an mcu for the stepper control itself, and one can do all kinds of microstepping since l293d is simply only a h-bridge and all that microstepping 'intelligence' is done in the mcu itself
the more elaborate stepper drivers some of them cost more than common arduino mcus and a h-bridge even for that matter the l298n