I don't think that's true. Some years ago I did a free trial with them (did not pay anything). More recently I decided to actually sign up (for a paid account) and the email address I used for the free trial years ago was not available. I eventually got that username only after contacting support and giving them the date on which I started that free trial, to prove it was me.
Some of it has to do with changes to browsers’ acceptance of cookies. If you need to set cookies on multiple domains you control (common for SSO), you used to be able to do it by loading a pixel image or tiny script from each domain. Now, however, that’s considered a third-party cookie, and rejected by many browsers. The only reliable way now is to redirect the whole page, and then redirect back.
tasting the rainbow