You're fairly delusional if you think most people's interest in open source stem from an ability to tweak the code themselves. It's simply false that most people can modify FOSS "all they want" as only a small minority have the ability to do so, and even in this group most won't have the time or resources.
yet some how GNU has been out there since the 80's and Linux since 91. For the average user means not being under the large SW companies thumb and whims