Snaking a clogged tub drain
Because the standard tub drain has a sharp right-angle T junction where the overflow and tub drain meet (this is also where the stopper is located if the stopper is operated by a lever on the overflow plate, as opposed to an in-the-tub stopper or rubber stopper over the drain.)

The sharp right-angle is not friendly to snakes passing, and the stopper, if present, even less so. Coming down the overflow is, on the other hand, a straight shot, and the stopper comes out with the plate if it's that style of stopper, so it's not in the way.

I highly recommend using a hair-catcher over the tub drain to reduce this problem going forward - a little more frequent easy cleaning of somewhat less disgusting collected hair .vs. dealing with the gunked up mess collected over a longer period in the pipes.