For example, Samsung has a device management Knox on the phone that allows telco to lock mobile services, control certain functions on the phone to prevent access but not gain access to the phone content. This functions are meant for company to control their staff company phone from leaking info out when it is lost. I heard for Android some features cant work if on mdm and some banking apps wont run.

I think blame those scammers who sign up for the phone and change hand sells it + not paying their installment. I believe the fraud case is very high triggering telco to implement such control to discourage resell during installment period.

Every good thing + abuse => inconvenience follows ...

I think the “discount” you get comes with the control. Question is whether you willing to do the exchange.

If objective is to take phone, runaway and default payment, need to find other telcos to do it …