One of the reasons they wouldn't do it is because emulators and ROMs are already rampant on PC and mobile (less so). So the idea of all of a sudden releasing a bunch of classic games in your pocket is heavily diminished.
Then why do many other game developers and publish make PC ports of their old titles which use emulators?
Why is Nintendo different?
That you can emulate old titles for free isn't stopping people paying for them, clearly.
So to answer your question - because those businesses have looked at the financials and decided that the lost potential sales due to people who use emulators are worth the effort do develop games. Nintendo has decided differently. It's possible that the other publishers weren't simultaneously pushing a hardware platform which also comes into play.
I never said emulation prevents all people from paying for virtual consoles. I simply was pointing out that it diminishes the value. For example, if Nintendo released virtual console on PC today, I wouldn't buy it when I've already got emulators and raspberry pi's running arcades. If there was no way for me to technically play emulated games and VC was released on PC - I'd buy it immediately.
So there ya go. One lost potential sale, how many more?