There is a considerable problem in enterprise software where trivial features are enormously expensive. If you hide all of the useful authentication features behind thousands (or tens, or hundreds of thousands) them don’t be surprised when somebody scoops you.
Value add needs to be more like added value than ransom.
If you have any emotional response like that it's 'ransom', then you're probably not the target audience for the enterprise tier.
(And I don't mean that you don't need/can't make use of features hidden in that tier, just that if there are many in the same boat, then the provider misjudged the contents of that tier.)
Free for some to use under certain restrictions. Therefore not Open Source (which is totally OK, I just want to make sure there's no confusion).