It's one way FCC does enforcement.
IANAL, but from what I understand, revoking a valid license isn't easy. There has to be solid evidence of rulebreaking and the accused has a lot of rights and defenses. FCC just can't yank licenses; this is to protect the innocent.
Renewal is a different game for some reason. Usually, simply having a clean record is enough for FCC to routinely process a license renewal. But when there is doubt - any doubt - the FCC can require all sorts of testimony and evidence before a license is renewed. FCC doesn't have to renew a license unless and until they are convinced the licensee will follow the rules and act in good faith.
Ever notice how, when a broadcast station license is up for renewal, they do PSAs about contacting the FCC if you have any issues? It's kinda the same thing for hams.
Usually the licensee can keep operating while the license review process is ongoing.
Remember always that an FCC license is a privilege, not a right.
73 de Jim, N2EY