maybe the picture of the business model of these large companies is not correct.
These audit firms basically proof, that your company's bookkeeping is "ok". That is a governmental requirement - need to have an independent verification of your records... I remember that the amount to pay for such statements vary in the range between 30.000 for fairly small companies up to several 100.000s and more.
Also, these large public accountants or auditing firms have a pool of headcounts (consultants), that they rent out to the market. Pay rates easily achieve 800 Euro/day, and go all the way up to things like 3500/day.
And all to often the clients order KPMG/Deloitte/PWC/EY to proof/verify their books, and at the same time place an order for the temporary hiring of headcounts from these companies.
I wonder how this can be an independent statement in the sense of a 4 eyes principle.
Today we know, that the figures of Greece have been "formed" in a way by Goldman Sachs and accounting firms, so that Greece can make it into the Euro zone.
Maybe today there is a rule, that you cannot hire for the next 10 years headcounts from such company, when they verify your books.
But probably the world is a much better place than I am thinking here
So their business model will change a bit, when blockchains will be used to keep track of your record, but that does not change the business with consultants, they can proof than something different :-)