Thats an assumption, thats not really true. Probably based on your own needs. There where dozens of people on the PSR tutorial forums looking for exactly this in an arranger.

Its Yamaha's aim to sell more Genos to different groups of musicians, and to do so they have to add the things the none typical arranger player likes.

Thast been the whole point of this discussion from the start,

I dare take it one step further. IF someone would add an arranger in the form of the Ketron launchpads to any Workstation, it would sell like nothing else before..