I think this comes down to two things:
If we define "polish" as: consistency+predictable UX+aesthetics
1. openness involves interoperability, and polish is more expensive to achieve when interoperability is a requirement
2. the primary market for polish tends to value exclusivity, which—while not entirely contradictory to openness—tends towards non-openness
The combination of these two means that when you focus on polish you end up with a product line that is likely to be non-open.
The fact that the primary market for polish also tends to be economically comfortable also conveniently leads to margins that allow for privacy, but I think this is just a happy accident.
It's my belief that if we want a private + open platform we need to:
- Accept very large sacrifices* in polish because doing both is only economically viable when catering to a market that doesn't want/need openness
- Choose a different economic model where resources are available to do both simultaneously.
* Also worth noting that sacrificing quality and/or UX can lead to less privacy given that privacy depends on security and security depends on both quality, and also on UX to prevent social attacks.