Commonly used for scams, carriers will frequently filter messages that contain shortened links and any significant volume can end with the number being blocklisted.
For business/promotional campaigns they don't want the end content obscured at all.
(This is from personal experience running SMS newsletter blasts, they really hate services like bit.ly)
That's really nice to know JoeCool, thanks! There's a fair amount of struggle with the carriers trust scores. Overall, there's an inclination to keep the SMS OTP (so that people don't create hundreds of accounts with the 2 free links) but offer the option to switch to email or WhatsApp once the link is created.