I would say it is extremely common if: The company sells something where development needs a _lot_ of domain knowledge AND the employee is a subject matter expe

I would say it is extremely common if: The company sells something where development needs a _lot_ of domain knowledge AND the employee is a subject matter expert in said niche domain knowledge. In this situation a lot of the top people will just keep doing stints anywhere between 2 and 7 years bouncing between major competitors in the field. Pharma, Automotive, Semiconductor fabrication, are good examples of this. Arguably in some countries where the law allows it non-compete terms may limit this.