@Canageek It avoids encouraging bad behavior: you're not penalized for posting links (esp. non-shortened links). Someone else's choice of a long URL doesn't eat up half of your message space. Etc.
It's been this way since April 2017.
(There's a similar reason that text you put in the image description field doesn't count against you. "Here, do the right thing. It won't eat into your message.")
@jond make sense, and you already can't assume how long a post will be since different instances have different length limits.
Cybrespace is an instance of Mastodon, a social network based on open web protocols and free, open-source software. It is decentralized like e-mail.