The pricing policy is more obnoxious than the price itself. $390 (or $590 for "maintenance and support") gets you the ability for one single developer to do any kind of work with it. The next tier is $1,500 (or $2,250 for "maintenance and support") and gets you the ability for up to 5 developers to do any kind of work with it.
Having to pick between (A) sneaking around behind your vendor's back to violate their licensing terms by having more developers work on it than you paid for and (trivially) concealing that from them, (B) paying $1,500 instead of $590 (!) just so more people can legally work on it, and not even getting support, or (C) micromanaging your team such that literally only one human being can actually work on that part of the code base...
...makes for a real bad customer experience, which is surely to the detriment of sales.
As a freelancer, I disagree that the pricing is obnoxious, it seems like a fairly typical business model for programming components. I view the 1 developer licenses as more of a discounted version for one-man shops like myself.
If you were going to violate their license you just wouldn't pay for it at all. It's free for academic and noncommercial use and you can download the complete library right from their site.
Corporate environments tend to have tools to manage seat-based licensing and smaller companies only have a handful of developers anyway. Typically the number of developers who need to be working with a specific tool is known when you start the project you're buying a license for and upgrading your license isn't exactly tough. I convinced my boss to buy our department a 5 seat license for Highcharts (without support) after doing a pretty exhaustive search for free alternatives with all the features we need and it has been great so far.
Of course there are steps between (A) and (B) - you can choose to purchase two or three Single Dev licenses. If you need four Single Dev licenses, you are better off buying the 5 dev package.
Having to pick between (A) sneaking around behind your vendor's back to violate their licensing terms by having more developers work on it than you paid for and (trivially) concealing that from them, (B) paying $1,500 instead of $590 (!) just so more people can legally work on it, and not even getting support, or (C) micromanaging your team such that literally only one human being can actually work on that part of the code base...
...makes for a real bad customer experience, which is surely to the detriment of sales.