How does having a cross-platform system make their servers or systems preferable?

I'm all for it and see Java as doing quite a bit of good (despite the terribleness of the language and brain-damage it's inflicted on developers, which is a great bit of bad). I just don't get how it helped Sun, and I suppose, history shows it did not.

By increasing the ease of writing stuff that needs servers, the idea was that more servers would sell. Some (not all) of those would be Sun servers. That's a net win for Sun.