At the NFL level the rule moving back the extra point in 2015 was a big part of it. Conversions going down from 99% to around 94% since it’s implementation definitely affects the percentages.It's usually a little less in college than in the pros. But like I said, they both change from year to year.
I believe the "real" break even point, given how often teams make two pointers and how often teams miss extra points, is in the high 30s, like 37-38%. If you can make more than 37% of your two pointers the math says go for two after the first touchdown.