To this day plenty of documentation refers to STARTTLS as being the preferred way of configuring your email client. This is _clearly_ insane in the face of implicit TLS existing. I've never understood why STARTTLS is recommended over implicit TLS.
Nowadays, it's often the reverse. Many clouds block outgoing port 25 by default, and sometimes even 587. But almost nobody blocks port 465 -- the assumption is that if you're using 465, you must be authorized to use that server -- so that's the port you must use if you want to send emails by SMTP from a typical cloud server.
I suspect the bureaucratic overhead of needing to go to IANA to reserve a new port might have had a chilling effect. See:
https://www.iana.org/protocols/apply
https://www.iana.org/form/ports-servicesWhat wasn't because of corporate firewalls. :)
It's even easier to fall for these shenanigans if you know just a little bit about security and heard that TLS supersedes SSL.
Using correct terminology would've led to tons of unnecessary helpdesk calls because Microsoft messed up its naming scheme.