Because it's a relatively large JavaScript library. Total line count is in the several hundreds of thousands.

The file in question is for this class http://jgraph.github.io/mxgraph/docs/js-api/files/view/mxGra....

1) It's the main public API to the the library, there's no logical way to split it.

2) We'd have a couple of thousand, very-annoyed-cos-they-paid-quite-a-lot-for-it customers, frankly, go apeshit if we split the file and broke their app on the next update because we wanted to switch IDE...