I think the idea was to get a jump on All My Children and Days Of Our Lives; for a little over a year in 1980-81 all three soaps were on at 1 (ET). Ryan's Hope was beating Search For Tomorrow (still on CBS), and The Doctors on NBC was past its peak; CBS had to figure that neither was so formidable that they couldn't be taken. As for AMC and Days, well, they were among the most popular soaps, so it was more valuable to CBS to top both of them. By putting Y&R at 12:30, it would be in progress when AMC and Days came on, and its viewers would be less likely to change channels. Having Bold and the Beautiful at 1:30 was the same strategy; AMC and Days would be in progress, and CBS viewers would be less inclined to turn away.
One thing I don't understand is why ABC doesn't do a split feed of GMA3. It airs at 1 (ET), noon everywhere else, and ABC affiliates in the earlier time zones have to run their news at 11 AM (WFAA Dallas, for example, was running All My Children at 11, followed by news at noon; GMA3 forced them to move the news to 11 so the network show could air at 12.) The Eastern time zone would still see GMA3 at 1 (like CBS's Eastern affiliates see Y&R at 12:30), but everyone else would have the choice of GMA3 at 11 and news at noon, or vice versa (like Y&R outside the Eastern time zone...11 or 11:30 AM).