Publishers are aware of trends in technology, and are struggling to adapt, like everyone else. Many produce ebooks, and all of them make use of the internet and online communications to present, promote and market their books. Reasons for insisting on paper submissions are simple:
- Even the smallest publishing company receives more submissions than they can process. Most do read at least a little bit of each one, but it takes time. Having submissions come through the mail tends to slow the flood of proposals and manuscripts.
- For whatever reason, people tend to be a little more careful with work on paper than they are with work on screen. Asking authors to submit by mail tends to force them to take the process a little more seriously, which results in a higher quality of submissions.
- Email, despite its many conveniences, is not foolproof. Messages fall into junk boxes, get lost, and accidentally get deleted. Snail mail may not be perfect, but it's easier to keep track of something that can be seen and touched.