This comes down to 'accountants' and 'budgets'.
Accountants don't like variables so always try and have fixed costs.
Suppose a job varies in cost from 50 - 500 quid.
An accountant would have difficulty budgeting for that coz it's variable.
So, tell them it's 1000quid fixed and he'll be happy coz he can budget it.
The more that FD's and bosses want to 'know' the future, the more this happens.
So, IMO, it serves them right ... ( 2 fingers etc )