You asked; we listened! After receiving numerous developer requests, the API team added a route to create teams via the API. Here are the relevant docs.
tl;dr
To create a team, make a POST request to /teams
with the relevant details in the body:
{
"data": {
"description": "All developers should be members of this team.",
"html_description": "<body><em>All</em> developers should be members of this team.</body>",
"name": "Marketing",
"organization": "123456789"
}
}