So bullshit jobs are a tax paid by big corporations? Why are they willing to pay this tax? If most of their workforce is improductive, why not get rid of it altogether? Why do these jobs exist?
Because corporations aren't monolithic rational actors, but rather large bureaucratic bodies made of people who operate in a broader social and cultural context.
One example is efficiency. "Why," say the optimists, "would corporations continue to employ more people than they strictly need to?" Implicit in the question is a characterization of the corporation as a rational, singular entity.
And I say that 'optimists' ask this question because one of the large questions that some smart people ask is "where's the massive productivity increase that (one supposes) would accompany a surge in jobs-reducing automation?"
But if we just move down the chain a bit, and re-ask the question in terms of the actual top-down management of these companies, conclusions present themselves. And it's basically that hierarchical, traditional organizations may be bad at reaping these benefits, and they may need to be killed off/severely threatened by newcomers to change their ways.
There are a lot of unnecessary jobs hanging around, for totally rational reasons. Ask yourself:
"Why would any particular manager prefer to have more people working under him, rather than fewer?"
"Why would a Department Head with many direct reports not be eager to work with another Department head to closely co-operate in a way that reduces both headcount and duplication of management effort?"
"If a certain corporate fiefdom is becoming more efficient due to automation in certain areas of its operations, could there be any motivation for the manager of that fiefdom to expand other areas of his operations instead of passing on the full benefits of that efficiency in the form of a possibly-reduced budget?"
It should be clear to everyone that we are being limited by the structure of the organizations themselves. And we are seeing increasing activity in self-organized companies, cooperatives, etc, at the fringes (and also of extremely-integrated larger companies like Apple under Jobs, which is an old-model solution to the problem of the inefficiencies inherent in very hierarchical organizations).
The newer-model organizations may be better able to reap the benefits of automation.
TL;DR: humans used to be increasingly necessary as wet robots for manufacturing, and then largely moved up the food chain to bureaucracy when real robots made the wet ones inconvenient. Mostly-unnecessary jobs have more-or-less stuck around because of the limitations of organizations, not technology.
Because most industries are consolidated by oligopolies. If newly formed, smaller and far more efficient companies begin to seriously threaten these oligopolies, they simply throw their weight around via acquisition, regulation or other quasi-legal means to destroy them.
Doesn't make for an exciting and optimistic story, but it is what it is. Pure capitalism is just as impossible as pure socialism, due to the exact same moral hazards. Human beings tend to use power to leverage their advantages in any way imaginable, regardless of the prevailing laws and ideologies of the day.
Hierarchy and structure has costs. Maintaining hierarchy requires inertia and increased transaction costs. Capitalism is predicated on hierarchies and market structures. A lot of jobs exist just to prop up the order of things.
I can think of one easy reason from a micro-economics perspective. A firm has "organizational rents" from being more productive as an organization than the individuals would be in aggregate on their own. This begs the question of how to divide them. The answer is usually along the lines of having a hell of a lot of political maneuvering to assign as much of the extra value to yourself as possible - salary, prestige, power, and favors.