Some really good comments here. It definitely all depends on the frequency band your phone connects to. At lower frequencies such as 700 megahertz with skinny channels the 5G speeds will be no better than 4G and LTE. However, at the higher frequencies like 2.5 gigahertz, 3.7 gigahertz, etc. and up into the millimeter wave, they are super short frequencies and do not penetrate walls and stuff well, but are way faster. This leads to tighter tower grids in order to penetrate buildings with that higher frequency. That also means less people per tower taking up your bandwidth. A tower that can go 10 miles (700 megahertz) will have a lot more users on it than a tower that will go half a mile for example.

Edit: Another thing is that tighter tower grids make for better wireless emergency alerts. Imagine a tornado warning being sent to a tower that covers 10 miles. Every one in that 10 mile tower footprint would get the warning. Whereas typically tornadoes are tiny. And a tower that covers half a mile getting a tornado warning would mean that that tornado is a lot closer to you.