Ahhh I see. I've never owned a Mac and for reasons like this never will.
Anyway, while arrows will help those who use a Windows mouse on a Mac it won't do much to help WT navigation for those who have hundreds or thousands of WTs. It's not really efficient to arrow (or mouse wheel) one WT at a time through a large list.
Looking for a particular folder or a WT inside that folder can cause the need for a lot of scrolling due to the WTs and folders displaying vertically.
As much as it pains me to say this since I have no need for a WT Browser but I think it might be something worth adding in a future update.