As an outsider to the npm ecosystem, reading this list of packages is astonishing. Why do js people import someone else's npm module for every little trivial thing?
Not Java, thankfully! Libraries containing 1-2 trivial classes do exist, but they're an exception rather than a rule. Might be that the process of publishing to Maven Central is just convoluted enough to deter the kinds of people who would publish such libraries.
It is, but it's still firmly controlled by Microsoft, particularly when it comes to ecosystem evolution. Some people find that uncomfortable even if the source is open - legal right to fork is one thing, technical ability to do so and maintain said fork is another.