Actually, many places you need to be registered to a particular party to vote in the primary, which actually might be more important as you are actually selecting the candidate..

Registering as an independent, leaves the selection process up to the registered party members, or those who are motivated enough to get out there. Those folks typically don't necessarily look to out forth a candidate who's moderate, instead you get, Trump, Clinton, Sanders or Cortez.

There's something to be said for registering to a particular party to select a proper candidate.

The stigma associated with being registered to a particular party leads many to register as an independent, which means their voice generally isn't heard until the candidate is chosen. It's unfortunate this data is public, it's even more so that politics has become so much of an identity for people that they can't see past it.