I don't where you clean Robert but I have never come across anyone who actually likes the pattern left, we would never leave the cleaning pattern in the carpet, the job in my opinion is not complete until the pile has been dressed.
A grooming brush is hardley an awkward tool,( although I have come across a few of these in my time.

) and grooming only takes a minutes.
I can not agree with you that has no benefit to the customer it certainly does, as already mentioned it aides drying times and enhances the look of the carpet of completion, indeed some carpets including most 80/20 's Axminsters and Wiltons recommend grooming after cleaning.
I am surprised that there are still cleaners out there that
dont groom but each to their own and if that's what your customers want then fine.