Wolfram Engine is not an IDE, or a photo editor, it is a programming and runtime environment so you can't compare these things. They exist in different worlds. If you want lots of money for people to even use and learn your language, you have to provide a free alternative to get people onboard. You can choose not to, of course, but they you will limit the reach and the importance of the product.
(No, being able to use a sandbox is not sufficient to properly learn any language because that's not how you use languages to build stuff)
And before anyone says how important Wolfram Engine is and that this is the going rate for specialized software: nobody cares. Because you are probably wrong if history is any guide. Lots of software used to be niche software and isn't today. Things change. If it's expensive and only available at a steep price, then only those who need it will buy it. The curious will get their kicks elsewhere.
There used to be a time when database professionals stomped their feet and yelled if you suggested Oracle might consider a Linux port of Oracle. "Impossible! People who use Linux aren't into paying for stuff!". And then it got released and then Linux became its most important platform.
Things change.
In order to get people to include it as an infrastructural component you probably have to ensure that it is free for non-commercial use. I'm not sure if you have to open source it. I use lots of stuff that is free for non commercial use - and then I use it commercially and pay for a license. Occasionally really expensive licenses.
I've looked at Wolfram Engine a few times, but in the end we never used it because it just didn't have a great enough following among programmers. I couldn't just tap into a talent pool when recruiting. It was hard to find experience.
I tend to choose tools based on the _people_ I can find to use them. In fact, usually the people I find choose the tools. That goes for how I choose languages, software, cameras, cars, motorcycles...you name it. No vibrant community means I don't buy in. And sure, there are lots and lots of cameras that are better than mine in that price range. But the cameras are not all that important. The people are. Who I can collaborate with, who I can learn from, who can help me solve problems.
Also, it tended to be a bit on the expensive side for what I wanted to use it for. Sure, I could have contacted Wolfram and said "look, we want to use it for this, but the licensing model doesn't quite fit", but how many developers do this?
(I remember thinking about buying Mathematica several times to tinker with it, get to know it and then perhaps see if I could use it for something. But it was expensive, and I'm not spending that amount of money for something I'll maybe going to play a bit with and then perhaps forget for a year. This too makes Wolfram Engine a bit of "interesting, but I'm not going to invest time in it".
And I can't say I've ever blamed Stephen Wolfram for it. He has a product that makes a bunch of users happy and him rich. Who am I to tell him that he should do things differently? So he exists over there and I exist over here and everyone is happy.
I'm excited about this change. I wish it had happened sooner so it could have had more of an impact. It certainly put Wolfram Engine back on my radar.