IMO: Don't forget in the beginning of 1970, Emission level was getting tighter it was coming into play.
That is why a 283 was replaced with a 307, 327 was replaced with a 350, 427 was replaced with a 454. And the 305 has a smaller bore but same stroke as the 350. It seem the longer stroke motors produce less emission. Chevy was in a hurry of building 302 for trans-am racing that was limited to 305. that's another story. Because of cars were getting heavy chevy needed a longer strokes motors in order of getting more torque.