X86 has an incredible amount of cruft built up to support backwards compatibility all the way back to the 8086. ARM isn't free of cruft, but it's nowhere on the same level. Most of that isn't directly visible to customers, though.

What is visible is that more than three companies can license and manufacture them. The x86 market has one company that owns it, another who licenses it but also owns the 64 bit extensions, and a third one who technically exists but is barely worth talking about. It's also incredibly difficult to optimize, and the people who know how already work for one of main two companies (arguably only one at this point). Even if you could legally license it as a fourth player, you couldn't get people who could design an x86 core that's worth a damn.

Conversely, ARM cores are designed by CS students all the time. That's the real advantage to end users: far more companies who can produce designs. If one of them fails the way Intel has of late, we're not stuck with just one other possibility.