Because the FOSS generation feels entitled to be paid while refusing to pay for tools, which leaves the typical enterprise customers as the only place one can make money with development tooling.
The thing is, as a person I don't want to feel ripped off. I don't subscribe to JetBrains since my work doesn't require these tools (also, I use Eclipse for 15+ years and it works well). The subscription culture allows developer to pump features indefinitely but, I can't subscribe to all tools that I like.
There are many services that I subscribe too (Dropbox, Spotify, Netflix, IFTTT premium, Evernote, etc.) but, they give me a service which touches my life everyday. I have no budget to subscribe to a tool to test for a year. It's not feasible. I need to eat.
So yes, I'd rather have a good FOSS tool which doesn't want $100+ from me every year and I'd rather patch it myself. But, if you provide me a good service which I can't replicate easily, or don't want to manage myself, I'd pay you good money. I'd be also very happy if the tool I'm paying is FOSS.
Also the biggest obstacle driving me away from paying is the tools are closed source and I'd be locked in if the tool/company lets out the magic smoke. All the services I pay are not locking me in. I can get my data out of them. So it's not always wanting to earn money for free.
I agree that intellij and eclipse are similar, but as soon as you work with C, C# or Python, there's very few good open source alternatives.
I write C/C++ and Python mainly. Eclipse CDT and PyDev are very good. Since I'm using the platform for 15+ years, I've seen its bad days too. Except some edge cases, CDT is bulletproof and works very well. PyDev is also very smart and helps me the way I need.
Actually, Eclipse has the best and most sensible Git UI I've ever used. I also like Tower but, Eclipse both makes sense and helps a lot in the relevant places.
One question on eclipse. Did eclipse finally sort out git/svn support?
Here's an interesting tidbit of history for those who don't know. One of the main drivers for the decline of eclipse was the complete lack of support for source control, which is a pretty basic feature for an IDE.
You could try to get some plugins. There were 2 major plugins for SVN and neither worked half the time for no particular reasons. It was a complete shitshow. Don't even think of doing that in a company where HTTP access must go through a proxy.
Developers eventually gave up and moved to JetBrains IDE. Source control worked out of the box.
Heck, I've developed my whole Ph.D. with it and it interfaced the tools that I need to use well, was stable and fast. When I pressed a shortcut, it did the thing I expected it to do. The whole experience was, well, uneventful.
I've used Subversive IIRC during my Master's and it was uneventful too. Didn't lose any data, the plugin didn't misbehave or had any problem with it. Was using Assembla's SVN + Redmine bundle as my remote repository.
The git support was similar. I just installed it and it worked. Still works. As I said before, they've nailed the best logical view for git IMHO. IIRC, now it comes bundled with the Eclipse.
They may have done some things wrong in the past but, it's a solid IDE and I like working with it. I don't think they deserve the strong words you choose, but to each his own.
Of course, your mileage, taste and views may vary.
I think that might sap some of the impetus to reinvent those features in a competing open source project (they can of course just copy them if they wait), and also might entice people to pay that wouldn't normally because they don't want to get on the paid product train. Users also get a known date a feature will be available, a real date, not a projected delivery date.
In a lot of ways it's what many companies that develop products do already to allow people to get familiar with their product (have an open source version with less features), but this allows them a better story, makes users feel more sure about what's going on, and if they release the code immediately but it's unusable for a period by other projects, that does make it harder for those projects to cleanly reimplement unless they're sure they haven't seen in (that might be a net negative for the public with a litigation happy company).
The hard part would be tracking the time, but git has ways to make that pretty simple.