Why do Evangelicals think that it's okay for them to follow "man-made" traditions but for Catholics it's not?

The only correction I'll make is that Catholics do not follow man-made traditions whatsoever, whether it would "okay" or not (which it isn't anyway). Otherwise, I agree with you. The Bible never claims to be the sole authority, a man-made tradition that originated with Protestants, yet they try to twist it on Catholics by attacking our Traditions (big "T" traditions) which are solid dogma that originates with God, not us.