yeah unfortunately it doesn't add any additional reach, it just makes your size category b i g g e r.

That being said, a L A R G E Bugbear is definitely not something anyone wants to run into. Buggers are already surprisingly sneaky for their sizes; making them bigger just makes their stealth more startling.

Edit:
In my Sunday real-world D&D games, I have an NPC monster in it who's a Bugbear. He wields a specialized pair of axes on chains, allowing him to swing them like whips; I also give him the PC Bugbear reach, so he's swinging his axes 15 feet of melee threat range. He's also a mounted warrior, riding a Dire Aurochs. So yeah, I have some measure of terrifying bugbear stories meself.