The part of 5G that gets thrown around a lot with high speed and capacity is mostly based on mmWave bands(think 10's of Ghz) which attenuate incredibly quick. Most of them are nearly direct line of sight. You already see some issue with 5Ghz wifi not going well through walls, there's a high chance you'd be falling back to one of the lower speed bands inside.

The other thing is there's a non-zero amount overlap in the way spectrum is used in wifi and 3/4/5G, MIMO, spread spectrum and other approaches are all trying to get as close to the theoretical limit of the channel bandwidth. When you start looking at large scale wifi deployments it starts getting split into cells of channels not to dissimilar to cellular deployments. There are some differences and certain bands benefit from discrete allocation/cell management but at the end of the day it's all radio waves over the air.