In London the argument for companies being in zone 1 is that meeting with people from other companies is easier. So for the few who have external meetings the entire company has to drag itself every morning and evening through the overcrowded, unpleasant London underground, arriving at work late, flustered, or miserable. What a way to start the day. If the companies moved only slightly out of centre, zones 2 or 3, the majority would be happier, and the few who meet outside would have a 10 or 15 minute, relatively pleasant, tube ride to get to a meeting.
Locating the office in zone 1 also allows people to live in lots of outer London areas. If you site the office in zones 2/3, you have to choose which bit of zones 2/3, potentially meaning people have to move house or commute even further. It's a higher cost to the company, but gives them access to a larger proportion of the labour market.
