To my understanding, every time someone is hosting a service e.g. mysql server, there is always a server IP (or domain name) and a Port needed to reach the service (e.g. www.servername.com:3306).
By default, when you're accessing some site in your browser with
http:// in your URL, it means you're accessing
tcp/80 port. And in case of
tcp/443. You can override the port by adding
:<port_number> after the host name, as you already mentioned in your question, example:
It's totally depends upon application developer decision to host application in server with any choosen specific ports .
By common application hosted ports are 443 with few of them will still use customized ports for example TCP_8081 etc
Application team is responsible to create awareness among users to use domain name or URL with hosted ports to access application .