There are reasons why Audi and Merc are popular - they can be good fleet deals for lots of companies (it's complicated, but some car firms really do well in the fleet / leasing market).
But again on status - seriously seen this happen so many times...
Bunch of different grade managers choosing their cars, back in the day when a lot of company cars were all one brand, and you had a specific 'L', or 'LX' or 'GLX' model. Managers would go crazy if their 'L' or 'LX' car didn't reflect their status. Such a bloody ego thing.
Now it's more complicated as most company car drivers have more choice over a leased vehicle, so the status thing is a little bit more blurred (someone wants a hot hatch, and another wants a bigger exec car) but hot hatch can cost more than the exec etc.
Quite a few folks also have private lease deals for themselves, or they get an allowance from work.
Lease deals allow people to drive a much higher value car then they could afford to buy. Effectively they are paying 'a little bit over the odds' in order to drive a car that is 'a lot over the odds' of affordability. They are paying the depreciation costs of the car.
That way, you can drive a 50K car, that loses 20K in 2 years, just pay the 20K in leasing. However, when they get their next lease car, they pay another 20K over the next 2 years etc etc.
(The figures are hypothetical examples).