Good point. But if we notice, there is no new consulting company that has grown big like KPMG, Infosys, etc in the last decade. Is it because achieving that scale as a consulting company is no longer possible?
But depending on how you want to measure growth and define consulting, HP grew its services division in the last 15 years (so did Dell ~20years) or so and it went from nearly 0 to billions in revenue. They always had a little services revenue/work but not like they developed in the last 15 years or so. A lot of large consulting companies you never hear about because they stay private and aren't in the "tech" sector. IBM GS grew in the billions during the last 15 years, even as they laid off people, proving the work is there to support that value.
One thing to note, consulting does best when economies are doing poorly to moderate. When economies are booming and employment recovering consulting actually goes down, when employment levels off at "fully employed" then consulting starts to pick up a little during a boom period. It makes sense if you think about it: it is much cheaper to hire a consulting agency to work on a project or add a feature when the economy is down as hiring FTE's would increase the burden on the business permanently. Both of my consulting businesses grew the most when the economy was doing poor, dot com bust was one time and the housing & overall market crash the other. We grew massively during those times and never did as well when companies came back to feeling good about the economy and growing internally. I say this because the last 10 years has been a more or less booming economy so consulting isn't doing as well during that time period, although it is picking up now with employment numbers being so low. But if you go back into the downturns you'd see differently.
Also consulting is a big field right, if you remove the SV/tech only bubble and look at the economy as a whole tons of defense businesses are purely consulting in nature and grew from 0. And quite a few hit over a billion dollars in the past 15 years. So just depends where you look.
I think if you look at the number of new product companies that come out that do ok but never reach a billion in annual sales and compare that to consulting agencies you'd find a pretty similar trend with similar percentages.
One other point. A lot of tech is defense phobic right now for whatever their reasons are, but if you look at almost every major large consulting firm that is large they had a staple of defense and government work, both within the US and outside. Ignoring one of the largest employers because you feel principled in doing so is completely fine, but you only add to the complexity of growth at that point.