Why does arXiv not allow numbered lines in submissions? I just tried submitting my first paper to arXiv. To be honest, this hasn't been an unqualifiedly fun experience.

One reason for rejection was that my paper contained line numbers. I am a bit confused as to why arXiv would reject papers for containing line numbers. One reason for me to submit to the arXiv was to potentially get comments on the paper - and it's a lot easier to comment on a paper that has line numbers. It's easier to discuss "lines 95-105" than "the third paragraph on page 5, not counting the table and its caption". I really like line numberings in papers I'm supposed to review.

Can anyone tell me why arXiv does not allow numbered lines in submissions?

(A quick internet search didn't turn up anything useful. )
In my experience, it is much more useful to give some context (a few words, name of the theorem, ...) to any editorial suggestions than line numbers. My documents exist as LaTeX source, so line numbers in some printed version don't correlate at all with line numbers in the text I currently work on. A few words of context are easy to search for in a text editor, line numbers would require referring to the printout to find same first. Besides, text changes (paragraphs get rewritten, shuffled around, new chapters are added, a new example appears, ...).