Easy. GPS. Wi-Fi is easy to replace by carrying a little more gear, whereas GPS isn't.
It's a pain in the backside to geotag photos without in-body GPS. If you use an external receiver, that's one more piece of gear that has to be continuously attached to your camera. If you use track logs, that's one more battery to keep charged.
Also, the precision of geotagging is likely to be better with in-camera GPS, because the camera knows when you pressed the shutter, and can get coordinates at that exact moment instead of on a ten second interval or whatever.
By contrast, it's not that hard to carry around an SD card adapter for my phone (to replace one of my uses for Wi-Fi) and a radio remote (to replace the other one). The batteries in a remote last for months, so they're a non-issue. And although radio remotes do require a device to be attached to your camera, you probably won't need to have it attached for every shot for days on end, unlike your GPS receiver.
Also, the alternatives to Wi-Fi work a bit better than Canon's Wi-Fi implementation, IMO, albeit at a cost in terms of the amount of extra gear you're carrying around. In particular, the EOS Remote app doesn't appear to support continuous shooting, unless I'm misusing it somehow. And because it operates in live view mode, focusing is slow, effectively giving you a huge shutter lag. With that said, it is still better than a timer.