They already do. For example, for containers you have 5 per host included in the Pro plan (I have more in my hobby projects...) and then you pay extra for each. Their pricing model is quite complex and with time you start to wonder if all these nice features are really worth that high prices.
They have to though, right? If you look at the nonsense people generate in logs, it would be a war crime to not monetize that. 20% of the PB's of data is probably the same 2,100 UTF-16 characters of Windows event id 4624.