I’d argue that LACs like the Claremont colleges also benefit greatly from a relative lack of competition. People interested in attending an elite liberal arts college on the west coast simply do not have many other options (most notably Reed, Lewis & Clark, Whitman, Willamette, and Occidental). The competition among liberal arts colleges in the northeast and midwest is far more stiff.
Similarly, there are not many strong private research universities on the west coast aside from Stanford, Caltech, and USC.