Linus Torvalds wrote a kernel because he bought a PC: hardware which allowed him to do anything he wanted.
Today, smartphones and mobile devices are much more popular among the youth. Could you imagine if Torvalds had been born in 1993? By this point, I'm sure he would have made something much less spectacular than Linux. Maybe he would make some pretty cool Facebook or smartphone games, and maybe a few cool web apps, but the freedom to tinker with hardware directly had been slowly slipping away over the past ~10 years. Since that avenue was becoming less available, there's a chance it wouldn't have grabbed his attention in the first place.
We still have laptops/desktops which aren't locked down. Hopefully that's what the young/future version of Torvalds would have gotten interested in. But how long until you buy a laptop only to find out that it doesn't grant you root access?