Because most users don't care whether software is open or closed source. They just want software that works.
And this is kind of true, isn't it?
If OSS wants to become truly mainstream the people creating it need to focus on the experience, not just the code
In a commercial app there is a requirement to make the installation routine simple because you have to sell the app. With a Linux (and sometimes just generally with FOSS) that drive isn't necessarily there.
It's a general FOSS problem; programs tend to lack that last little bit of polish that would "sell" them - but that is a ball ache to add in.
They want something that works and fit their needs. That's it.