For the same reason they included the INT unit in the first place, I suppose (it's more efficient?). This move (if at all real and not fake) would simply fix the FP:INT ratio. Because, right now in Turing there's nothing to switch to, nothing to schedule to the INT pipe in 64% of cases, since there's supposedly only 36 INT per 100 FP instructions.
Per Nvidia docs one of the benefits of the INT pipe is to initiate data loads for the next iteration of a loop while the FP pipe is processing the current iteration. Initiating data loads as early as possible likely leads to more efficient use of bandwidth across the memory hierarchy especially for tight loops with a high INT:FP ratio.
As you pointed out that's less helpful in other cases where the FP:INT ratio is high. Half the available register bandwidth goes to waste as there are no execution units available to issue to every other clock.
The pipeline latency on Volta/Turing also dropped to 4 cycles from 6 on Pascal. Not sure if that was also due to splitting out the INT pipe.