Nothing is wrong with hubs, but now there is yet one more thing you have to have available (at least until they become more prolific in external devices)

Want a legit answer? They lack power isolation. I had a device surge/short while attached to a USB hub (it was a branded one), and everything else attached died: Keyboard, Mouse, motherboard, and a phone.

This was back pre-USB 3, and the power limit of USB has only increased since then (USB 3, USB-C, etc). This means the wires get hotter, the hub gets hotter, and any short/surge will have an even more dramatic effect (e.g. fire?).

Honestly USB hubs should be up to the same spec as a surge-protector/multi-tap, but they aren't, even though they carry enough electricity to kill someone.