You should probably ask the question in reverse: why is Java seemingly so heavily criticised on HN when it is clearly an incredibly successful and productive platform that almost took over the whole enterprise world?

For its time Java was a god send. It solved a ridiculous number of problems that programmers today just don't even think about. We used worry about things like byte order when sending data between computers. We used to license libraries to provide basic things like lists, hashtables, string handling. Compiling things to work on multiple platforms was a nightmare, especially Windows. Developing on Windows and deploying on Unix was a pipedream. Java just swept all of this away and replaced it with a standard portable runtime that worked across Windows and Unix was free. The equivalents that offered these things (say, Perl) were not considered viable contenders at the time (dynamic languages in general did not gain a lot of trust until Ruby on Rails and PHP became so widely used - people just did not believe that you could build a large scale system with such languages and not have all fall apart if the type system wasn't rigorously checked).