Cal Poly’s plan was to increase enrollment. They were at mid-18,000 in 2012 and were shooting for around 21,000 to meet demand, but still meet their educational objectives. With the elimination of ED, their yield calculation was bad and overshot enrollment by about 1000 in a single class. They have been slowly backing that down to get back to their original intended numbers.
I believe the new dorms are simply an effort to replace old decaying dorms. It wouldn’t surprise me to see some of the older ones removed in the next few years.
Even if everything stayed the same, CP is ever increasing in it’s acceptance difficulty because more students are applying. Last year alone saw a 12% increase to over 65,000. That’s more than 20,000 more applicants than they had in 2012. As @Gumbymom said, “make sure you have several backup schools on your list.”