Since the release of GPLv3, technology pundits have been opining about how adoption is unlikely, usually citing Linux's still-GPLv2 status as (often their only) example. Even though I'm a pro-GPLv3 (and, specifically, pro-AGPLv3) advocate, I have never been troubled by slow adoption, as long as it remained on a linear upswing from release day onward (which it has).
Only expecting linear growth is a simple proposition, really. Free, Libre and Open Source Software (FLOSS) projects do not always have the most perfectly organized of copyright inventories, nor is the licensing policy of the project the daily, primary focus of the developers. Indeed, most developers have traditionally seen a licensing decision as something you think about once and never revisit!