It's to minimize distance. Aka factories minimize distance between inputs, other factories, and customers. So Coca Cola builds multiple factories because buyin

It's to minimize distance. Aka factories minimize distance between inputs, other factories, and customers. So Coca Cola builds multiple factories because buying water locally and shipping the finished bottle 10 miles is cheaper than shipping it 1000 miles. For car factories there are some costs for traveling in between factories so most of them are still clustered in certain states, but the factories can be spread out. Plus, once a city has too many factories increasing wages, the next company that comes along will build their new factory elsewhere. Tech offices have effectively zero distance to customer cost (at least within the USA, you might build another place for say the eu) So the main costs to minimize are input costs (employees) and costs between offices (coordination). Unfortunately the "cost" between offices is relatively high. Unlike multiple factories, aka ship the plastic bottle from one factory and the plastic cap from another factor to the main bottler factory, multiple offices require coordination with one another. Or to put it in tech words, it's not easily parallelizable. The more offices spread out in multiple cities you have, the more meetings you need to coordinate between each city. And the cost between offices is essentially "time" the most precious resource for a tech firm, which cannot really be removed. And so tech firms pay the higher col rather than spreading out into other cities; well until the col really increases too much.