CTA signals

I ride the CTA quite a lot between Howard and Fullerton or downtown, and when I can, I ride shotgun in the old 2400's with a view out the front. I've been noticing the CTA uses fairly standards signal indications, but here's what I can't figure out. State/Lake and Clark/Lake both have signals that prevent trains from entering the station when other trains are present at the platform. None of the Wabash stations do. Why is that? Is there an "Operate on sight" regulation?

there has to be a signal previous to the station but it does not need to be right before the station, it would hold the train a farther distance away. This may be dependent if the signal has a stop and proceed or permissive indication.