This may hold in the USA, but clearly not in Germany. If, as a subject matter expert, you do have the choice and can tolerate the high stress and high workload, big consulting firms typically pay much better.
The reasons why true subject matter experts nevertheless often work somewhere else are different:
- As I already mentioned: the consulting environment is very stressful and the workload is huge. This environment is rather not suitable if you have or plan to have a family.
- Consulting companies typically want to hire employees who are smooth salesmen first and subject matter experts second. Many real experts on some topic often rather tend to be more opinionated and "rough around the edges". So they very often don't get hired.
- Very often the daily job working at a consulting company is very different from the topics one is an expert in. Many subject matter experts prefer an environment where they can apply their skills better.
- For many subject matter experts, the topic where they really excel in is very narrow and specialized and very different from the topics where a consulting companies can easily sell "experts" to the customer. So, many subject matter experts don't get hired because their topic of expertise is not easy to sell to customers and/or is too niche.