That's definitely a plausible theory; I could certainly see Verizon possibly trying something like this in order to boost sales on Cellular Enabled Tablets.  But, disabling Integrated Calling would also decrease sales on their Cellular Enabled Smartwatches, because their smartwatches need the Integrated Calling feature in order to make phone calls as a Stand Alone Device (IE: Samsung Gear S3).  So if Verizon is willing to risk decreased sales in Smartwatches for increased sales in cellular tablets; then your theory may be correct.