^I have tried the guitar and I just can't do it. I've tried it left handed and right handed and it just does not work for me. If I want to play the game in a manner that's "boring" and I'm willing to pay for the game, why shouldn't I be able to ?
If you don't want it then don't buy it, but the developer is under no obligation to add a specific feature that is in this case probably used by an extreme minority. There's obviously a lot of custom stuff going on in how it handles input (the guitar has more buttons now then the controller does) so they probably decided it wasn't worth the effort to support a feature so infrequently used or requested.
You're not willing to pay for the game, you're willing to pay for a different