Do you really think HE owns most of the fiber they use? It's mostly leased from much larger behemoths that own the physical cables, who treat it as a private conduit for photons, and lack the ability to even know what's being transmitted over it, so can't censor.

Source: https://he.net/about_network.html - you see them talk about "negotiating with the top fiber carriers" and even "long haul wavelengths", which means they don't always lease a whole fiber, sometimes just a small slice of the EM spectrum on one.

IP transit is a value-add on top of an underlying physical asset which already has the properties that you want.