Why did the original logo get changed for the Baltimore Ravens?

This is one of my problems, but I also would like to know why aren't there more throwback uniforms for different teams. For instance, the San Francisco 49ers, the Dallas Cowboys and the Miami Dolphins get plenty of love, but other teams only have the home version of one throwback and the alternates should be there. For instance, the Denver Broncos classic uniforms for which they just resumed wearing just last year, should also have the away version and the '90s New England Patriots blue jerseys well, they too should have the away versions.