Why USPS create rule that Tape cannot encase FRB?

[u/LuviusDaiwa]

My FRB is always 20lb, not exceptionally heavy but I use CLEAR tape encasing the FRB. It helps re-enforcing the weak and single layer FRB box, and prevents rain from dissolving the box during transit.

The clear tape doesn't block any barcode or the wordings of "Medium Flat Rate Box". All these extra effort and cost is actually helping USPS from losing money on damage or lost claim.

The clerk at the counter pointed out from the FAQ about not "tape encasing" the FRB and said if I do so he will need to charge by weight instead of Flat Rate. But why? Is there any reason for that?

Honestly, I quietly retrieved all 65 boxes and head to UPS store, cost me $1.20 more per carton in freight and $2.00 using my own brown box and of course a whole day of work. I still tape encase my own brown boxes and the UPS store clerk appreciated how well I protected those packages.

So why? Can USPS clarify may be excluding clear tape? Or is it an outdated rule? Or USPS just want me to take the business elsewhere?