https://www.insidehighered.com/digital-learning/article/2017/08/30/umass-online-surpasses-100-million-annual-revenue-enrollment UMass is certainly a quiet giant in the online learning landscape.
The legitimacy of a state university system is a very powerful sales tool. While I'm biased (although I've never taken an online class through UMass, my M.A. was in-seat), I think any state university system could have the same success if they employed similar sales & advertising strategies.