URL design: is it bad practice to use consecutive numbering in URLs for user-submitted items?

I'm working on a website where users can submit items (in this case, proposals). The simplest URL design would be something like website.com/proposal/1, website.com/proposal/2, etc. (perhaps with a slug appended) but I've never seen this done in practice.

Is this URL design really as rare as I think it is and if so, why?

This URL design is not uncommon.

It is used, for example, by

• stackoverflow.com (for each post):
  1. https://stackoverflow.com/questions/1/
  2. https://stackoverflow.com/questions/2/
  3. https://stackoverflow.com/questions/3/
• Drupal.org (for each user):
  1. https://www.drupal.org/user/1
  2. https://www.drupal.org/user/2
  3. https://www.drupal.org/user/3

But there are various cases when not to use this design, for example

• when all/some URLs should not be easy to guess (example: YouTube, for unlisted but sharable videos)
• when URLs should not contain opaque/unneeded parts (example: Wikipedia)
• when it should be private which URLs/pages were created before/after
• when it should be private how many URLs/pages of this kind exist