Developers of these apps would have little motivation if the maximum audience size was cut down to the very few who would use adb. The ecosystem would die.
That uses a workaround based on WiFi debugging even though it's all local. It doesn't run if you're not connected to a trusted WiFi network, you have to set it all up when connecting to a new network, etc.
Not only users are not connected to WiFi all the time, but in many developing countries people often have no WiFi at home and rely on mobile data instead. It's a solution, but not a solution for everyone or a solution that works all the time.
And how do you estimate the audience that even cares about those issues?
I think number of people caring about alternative app stores, F-droid or whatever is very similar to the number of people willing to use adb if necessary, so rather small.
But the ecosystem exists, regardless of what the absolute number is, and it would be bad to lose it. If the platform was more open like Windows the ecosystem would grow, if it was less open like iOS it would die.
