Ask HN: Why do most platforms have the same host pattern?

A lot of platforms like fly.io, Heroku, vercel, etc. have more or less the same simple host pattern. The pattern seems to be:

  {random-string}{domain}

Some reasons are obvious like:

1. Using the same subdomain allows for a single wildcard cert 2. The random string label probably helps to avoid collisions, protect privacy, security, etc.

What other reasons would this common pattern be used?