Business relocation is actually very hard, and to a large extent it is the fault of working women.
FX:Ducks
In the "good old days". The man was the main wage earner, and the wife (no cohabitation thankyou), either didn't work or had a job to make "pin money".
Thus he could easily move with his job, and the wife could find another little job or not.
The idea that a husband would follow his wife's job was quite absurd for most people. And because many women did low skill jobs they could easily be replaced by locals.
That's not true any more, often the woman is the larger wage earner, and in the sort of "proper" job that is hard to move. Even today, most men would not move if their wife's job did.
Our transport system is crap, but it's centre is London, meaning that you can often change jobs without altering your home life at all.
But if you're in a specialist job in less economically active areas, there may literally be no other job at all for you without a serious house move.
Thus London cannot help but be a magnet for skilled jobs. There is no good reason for the ad industry or publishing in general to be in London, except that is where the staff are, but in an economy dominated by services that is quite critical.
The education system makes this worse of course. I cannot think of any plausible threat or incentive that would make me shift my kids schooling at the wrong time.
To make it worse, moving to cheaper areas is done, on the cheap. Most staff issue can be solved by money, but instead the "business logic" is to "normalise" pay to local levels determined by the HR department. And yes, this often means freezing pay until inflation makes you "normal" for the area.
Many staff aren't that critical to the business and can often be replaced, but of course there is a strong correlation between being very useful to the firm and being able to leave get a job that doesn't mean rows with your other half, screwing your kids schooling, the stress of moving (with little help from the firm), and a pay freeze for the next 5 years. (Oh yes, and covering for the people who left)