Commonly these decisions are tied to the visual aspect of the product design process. This is what gets talked about the most, anyway.
Designers hate when others mess with their creations, because the visual aspect is the most personal aspect of the product they are designing. It concerns personal biases, taste, and other things which make a design “theirs”, and it's usually best to leave it to them.
However, there are design decisions on a product level which exist at the same time, and they aren't nearly as visible (pun intended).
Product design decisions are much more impactful, and we use them in order to shape a product, to decide how a product will work and achieve certain goals.
A very interesting product design decision I was reading about is how YouTube incentivized creators to rely on their ads more. See, creators know people don't like ads. However, creators like money. So they decided en masse, to bypass the ads from YouTube and dedicate a part of their video to showcasing a sponsor's product. So if the creator is a cook, they will dedicate a part of their video to promote e.g. a cast iron pan which you can buy.
How does YouTube fight this?
It's genius, actually. You would assume that they would start penalizing videos with this kind of promotion—which does happen, by the way—or something along those lines.
What they did was something else entirely: they released a feature called “Most replayed”.
This feature overlays the video with a graph illustrating which parts of the video people are actually watching.
What it also does, however is that it's also showing the sponsored part of the video which people usually skip over, so it shows on the graph. And that's the trick!
By making the sponsored content visible in the graph, YouTube was basically allowing the users to identify the ad, and allow them to skip it more conveniently, which incentivized the creators to use YouTube's built-in ads.
It's brilliant, really. And it shows what kind of thinking you need to do in order to make product-level decisions which rarely have anything to do with what is traditionally considered design. Also, this is a great example why traditionally-educated designers with a background in visuals have a hard time in product.
These kinds of solutions require a holistic, cross-disciplinary approach, and can't be isolated by department. It's not a “design problem”, it's a product problem.