Avidyne tried to hire me a few years ago. They said their biggest obstacle was getting shops to carry and recommend their stuff. When people actually try it they are sold (I was). It’s better.
For the shops Garmin is an easier sell. Customers know it and generally accept it. It works well, and they’ve done a great job building an ecosystem of products that integrate easily. It’s a lot more work to sell someone on an alternate brand, and when they do they don’t make any more money. In fact if they are replacing a Garmin 430/530 they’ll make less since the IFD’s are plug and play.
Keep in mind that 60 years ago Al Meyers built a better airplane than Beech. Better doesn’t always win in the marketplace, but those willing to do the research and take a chance get rewarded with a superior product.