No reason, they're conventions. Check out this list and you'll get a better idea. It's simply a number that the developer assigns without a particular meaning. It's kinda like telephone help lines, one thing that a developer might want to try is to find a pretty memorable number while trying to avoid conflicts with other programs running at the same time.

[–] [email protected] 1 points 1 year ago

id say your telephone number example can be extended:

1800 is for free numbers, but why? no particular reason, just that’s the number that got chosen at some time… same with port 80 being HTTP: that’s just the number that got chosen!

you can also have an HTTP server running on port 25 (usually mail); it’s just bad practice… just like there’s no reason why your phone company couldn’t make a regular phone number toll free!

what’s pretty normal though is running an HTTP server on say, port 5000: this is just for more technical users though, because you have to know the port; your browser doesn’t “remember” it for you