From my home network google.com has about 120ms time-to-first-byte.

If I was on 4G add 20ms for the DNS lookup, 20ms for each part of the SSL handshake, then another 20ms for the actual page request. If the page requests additional resources repeat that for every single source and 20ms becomes a big deal.

For gaming (assuming 20ms latency and a 60fps game) that kind of a delay means that you are about 2.5 frames behind your opponents. In some games that really does matter.

I agree though that caps are bad for everyone, but that has nothing to do with the capability of the infrastructure and everything to do with perpetuating the illusion that there is a bandwidth scarcity to justify slow connections, shoddy service, and higher than free-market prices. The specs for 5G will never change that.