“You make more shidduchim”? Surely not. The modern orthodox/mixed crowd communities don’t have a greater marriage rate than the Chareidi/seperatist communities. Mixing genders in college or weddings does not translate into “more shidduchim” (higher marriage rate).
Secondly, considering the gedolim’s existing objections to college — even with seperate genders — you can only begin to imagine the gedolim’s opposition to mixed colleges.