So from the context of a non-profit, profit (as in revenue - expenses) is money to be used for future expenses.

So yeah, Mayo Cinic makes a $2B profit. That is not money going to shareholders though, that's funds for a future building or increasing salaries or expanding research or something, it supposedly has to be used for the mission. What is the outrage of these orgs making this kind of profit?

The word supposedly is doing a lot of heavy lifting in your statement. When it's endowments keep growing over decades and sometimes centuries without being spent for the mission, people naturally ask why the nonprofit keep raising prices for their intended beneficiaries