Maybe the reason we say something is "simply the best" is because simple is often the best route to take. In baking or cooking, we like to try new recipes with new ingredients , but we often know when we are not going to like something because it's now too different or complicated. The flavours or ingredients that I like is often,found in homemade (not always by me) fresh , simple, like bread, soups. I used to think that the foods I ate as a child were really different than other "Canadian" kids, they used mayonaise, I didn't even know what that was. After all these years I realize it was the simple ingredients that made it delicious.
Even in knitting, I gravitate to simple lines, classic patterns, Even if it appears complicated or challenging at the beginning there's a simple logic that unfolds and it totally makes sense.
Simple does not mean boring. Boring can mean that there is no excitement or challenge. But they are both to be found in simple. We use the term "simply the best" "simply delicious" "simple life" etc. There is order in simple. The truth is seen in simple.