> You’d need to ask the developers writing all these router OSes, smart televisions, Android phones, … whether they chose Linux because of its high quality or, I guess, randomly?

Or cost... or abundance of existing tooling for... or a ton more factors that are all considered. And quality itself is multidimensional. Something might be good for engineering flexibility but terrible for exposure to end users, or vice versa. And engineers can work around shortcomings much better than end users can.

OSes aren't like Javascript frameworks. There are only so many viable choices for a given domain. It's like if someone chose T-Mobile over AT&T and Verizon and you automatically concluded it's because of quality.