Three reasons why cities/'large conglomerations of people and technology' remain necessary,

Communications infrastructure still has large costs. Decentralisation is good, but the costs do increase, there is a balance point between the extremes. Lemmy and the wider fediverse is a great example of a search for that balance point.

Network effects, alone with my own thoughts i'm a scrub with a mug, together with others help those thoughts can become gems.

Company towns, an extreme but possible outcome, are a bad idea. It is a monopoly using geography and societal connections to reduce the competitiveness of your employee base.