A _lot_ of really shitty "web interfaces" which are actively supported/created/updated for enterprise products use java applets. They are universally pretty terrible (as are, in my opinion/experience _most_ user interfaces running on any JVM).
Lots of companies and lots of developers give lots of fucks about Java web UIs. Because Java programmers are commodity programmers. Everyone knows the language and inexperienced programmers can be productive in it without any great risks. (Not to say that there should be any strong association between knowledge and usage of JVM tech and competence, it's just anything that reaches that depth of adoption is bound to have lots of ... mediocrity)