I don't get all this hate against Microsoft because they suggest or prefer things they worked on as solutions, without actually tieing you to them. Do you work on software for years and then tell everyone to use something else?
If it was actually tied to their other services then I could see the reason to avoid it, but if using .net core without windows, azure, or sql server then I dony see how you are actually tied to it
Unless you want to be locked into a future centred around using Azure and Microsoft technologies, there are better, more open vendor-neutral languages with more diverse and mature libraries you could be building on.
Objectively, MS simply has done more work to create a comprehensive package. It would be a disservice to their customers to not increase integration between it all. For the longest time, this was Active Directory. Today it's Azure and .Net. Amazon doesn't control one of the most popular programming platforms to do tighter integration than already exists. Oracle does, but I've never really heard much about their cloud offering.
Microsoft has all the pieces, either it's appreciated or you can resent it. But they are no longer forcing you to use it, it's being sold on merit and I like what I see.
A good language is only part of what makes it appealing, having a large diverse open community is often more important as it ensures mature bindings are quickly available for new technologies and 3rd party API's, it influences whether the language will be used to create new technologies (instead of just playing catch up and making clones of what's in other languages), whether libraries are able to succeed on merit so it doesn't discourage the community to invest in developing a variety of competitive options and whether there will be an active community available to quickly answer questions and resolve issues.
.NET Core will never have the community of other popular languages, unless you're happy to use Azure and want to be locked into using Microsoft technologies there are much better platforms to risk your business on instead of committing to one whose future is controlled by self-serving interests.