I don't agree with the person's suspicions, but I can speak to your question.

If you're making over $1M/year or have more than 250 employees, you have to pay for Visual Studio or the C# DevKit in VS Code. Microsoft has been taking the open-core of VS Code and putting proprietary extensions into it. However, this isn't just C#. Microsoft has also replaced the open-source Python extension with something closed source.

There is an alternative to Microsoft's tooling with JetBrains' Rider. Rider is pretty amazing. It's much higher quality than any of the other JetBrains tools and part of that is that the .NET ecosystem is really amenable to tooling (and paying for tooling) and that JetBrains had been creating ReSharper for Visual Studio for a long time (so they already had all the .NET intelligence built out).

There was a thing where Microsoft was going to remove hot-reload from the dotnet CLI tool and make it only available in Visual Studio. I kinda felt like some of this was motivated by timing more than strategy, though. The CLI's hot reload had some rough edges and .NET has corporate style release dates with fanfare like .NET Conf. But the .NET hot-reload is quite excellent. Most edits can be hot reloaded and you can set it to simply re-compile and re-run for the ones that can't hot reload (and it just takes a couple seconds). It's dead simple to use and works (and the amount of time I've wasted to get hot reloading in Java is just incredible).

Really, every ecosystem tries to find some way to monetize. The creator of Elm has a great talk on this: https://www.youtube.com/watch?v=XZ3w_jec1v8.

Microsoft's monetization feels reasonably benign to me. If I'm bringing in $1M/year or have 250 employees, I can pay $500/year/engineer (or maybe less with volume or annual licensing; or $250-420/year/engineer for Rider for an organizational license). Sure, there are costs, but it's not like $500 is that interesting if I'm paying engineers $150,000/year. Likewise, Microsoft likes .NET as a bit of a halo project to get people into Azure. I don't use Azure at all and there aren't really Azure specific features, but in the same way that the iPod/iPhone brought a lot of people to the Mac, .NET probably brings some people to Azure. Even if you're a developer that knows better, you might have someone in your org who thinks "oh, it makes sense to deploy with Microsoft if we're developing with Microsoft." There's a lot of money up for grabs from that thinking. It likely also drives sales of things like Microsoft SQL Server. .NET works great with PostgreSQL or SQLite (and I'd assume MySQL as well, but I haven't used it), but I'm sure plenty of organizations pay for MS SQL Server with the "why not all from Microsoft" thinking.

So yes, Microsoft isn't looking for zero monetization, but the IDE license fees don't seem like a problem - either you're small enough that it doesn't matter or you're large enough that the fee is small. The rest of it is just stuff I can ignore (Azure, MS SQL Server).

But Microsoft's money often comes with some nice things. There's good documentation, a lot of great improvements each year, lots of great video sessions, and some truly amazing blog posts. .NET really has some amazing blog posts - and part of that is that Microsoft gives people the time to create some really high-quality content. If you haven't watched the Elm video I linked above, I highly recommend. It really talks about a lot of the things that money brings to a community. .NET comes with a lot of polish - more than I've seen in any other ecosystem and I've been programming a long time (and I've never been a Windows user).

If the cost of a healthy ecosystem is that companies with enough money to pay a few hundred dollars a year have to kick in a little support, I'm good with that. If I create something that starts bringing in $1M/year, I think it's reasonable to think I should kick in some money. I also understand others who don't like that - especially since it's kicking in money to Microsoft, not to some non-profit community foundation. But .NET feels practical to me. The money in the ecosystem means that a lot of high-quality stuff gets produced.