Besides treating a real number like some nugget of gold that can be resold multiple times to all sorts of bad actors (‘business’), there are practical supposedly honest reasons.
The security theatre of ‘authenticating’ you by ‘text’. 2FA scam
If you have questions and call, it is the fastest way to pull up records of the order and tracking. A 10 digit phone number is easier to understand over voice lines that a 32 digit alphanumeric tracking number the customer usually doesn’t have