I'm going to give an answer with full caveat that it's nothing but an educated guess...I have no inside info. It's location. For Summer Seminar and STEM specifically.
Do NOT equate this to less chance of appointment application because as everyone has said they're two different things. But your area of CT is likely higher income than most of country, higher awareness of SAs and therefore less ROI for marketing outreach programs like the Summer programs. Nothing more or less.
I get he is likely feeling disappointed, but try to keep it in perspective that it's a marketing program and not the end goal anyway (that's the appointment).
Wish you all the best!