Microcontroller manufacturers like to promote the use of classless bulk devices and CDC "fake serial port" devices because both of those types mimic the kinds of things that many developers used to do with old fashioned RS-232 serial ports.

It's almost as if they don't think you're smart enough to learn something new and better, yet which is actually easier to use.  (We think you are smart enough.)

With either classless bulk devices or CDC "fake serial port" devices, you not only have to provide a device driver for your end user to install, you also have to figure out what both the Host and the peripheral device are going to say to each other: that is, you have to write a protocol yourself.

So what could be wrong with that?