Not true, theres plenty of "average" gamers that want more performance which can only be achieved via MGPU, and can notice issues when they play. Most people dont want to have to mess around with 3rd party tools, finding the best frame caps and setting up profiles for each game. Many just want fast, smooth gameplay with minimal hassles.
I know plenty of pro and semi pro players that couldnt give 2 shiits about their hardware either, but will scream when its not smooth. They dont care about PC's, they care about gaming and want a trouble free experience. You see, most PC gaming enthusiasts are not computer hardware enthusiasts. Those are two different things.
It's also beneficial for both vendors to improve the MGPU plug and play expereience, meaning they can sell more hardware, instead of average consumers being put off by the issues and messing around required.
I dont see the problem anyway, whats it to you if both vendors improve in this area?