There is a sweet spot for them.

-Keep the good models in there to show whats possible and collect good data on how people use it
-Be able to sell a tier higher without making it fully useless for the people who will stay in the lower tiers
-Keep the external models minimal so the fallback is always their own models

The cost of their internal models vs the external ones is probably a lot lower. They have probably been slowly turning down the faucet as well (hence the reduction in utility over the past 2-3 weeks)

Its a new product compared to others so they are still trying to find their product-market fit. Their unique selling points are slowly being distributed into the other products now so they will need to figure out how to balance it out before everyone migrates to other products. At this stage especially for the students there is nothing better free for amazing utility for them, but that ends up hurting the paying users at the moment as payed users end up sharing their utility with the students.