There was a time when they charged for data points/performance traces ingested into the system. At our scale, we were paying around $100/month. We were prepared to scale that to their, I think it was, $550/month plan when our usage got that high.
They relatively recently changed their structure to charge per registered user. This would have raised our bill to around $1500/month at our current scale, to get all of of the stakeholders in there.
This is a cost incongruent with the value we were getting out of it. Even a ~$500/month price tag does not correlate with the value received, at our scale. It would one day (its a great product), but not today. So, today, we have two employees who have access to that, keeping our spend the same.
Here's the key component of this pricing change though: They will, no longer, be able to grow revenue with us. A pricing change forced us to make organizational changes. Those organizational changes mean that fewer people are seeing any value the product could deliver. When fewer people see the value, then the product has fewer advocates within the organization; its fungible utility will eventually be rolled into a competing product we already pay for, like Datadog, even if the experience is worse, because when we discuss Engine its always prefaced with "Oh, I think Dave in ops uses that, no one else does".