If you read through the content you'll see it's not an attack. It simply addresses some major flaws in W3Schools as well as some sketchy business practices.
If I ride on a boring, crappy rollercoaster, I don't need to open up my own theme park in order to air my frustrations.
A lot of the people who worked on w3fools spend a lot of time helping actual other human beings who need support in building websites, and encounter the errors from w3schools regularly, and we invest our time in those and other endeavours. W3schools said "we're going to spend OUR time on building an entry-level reference that everyone can use," and we want
a) the community to be well-aware of its caveats b) it to improve