i agree, but let me play the devil's advocate and argue that revolving doors might also play out well for the business.
The biggest fear (or risk?) a business owner might have is to be held hostage by a employee whose function/knowledge/skill is essential for business continuity. This gives the employee undue leverage, which lowers the profits, and allows said employee to extract close to 100% of the value they produce.
Therefore, a business would actually prefer a set of replaceable cogs rather than irreplaceable (but higher performing) employees. The business process could be adjusted so that the downsides of replaceable cogs is mitigated - such as strict processes or procedures and docs, or rely on technology that is can be easily hired for, rather than niche tech that would require finding a particular engineer with such knowledge of the niche tech (even if such niche tech is more productive!).
And this leads to the situation where employees' pay are market rate, but only at the time of hiring. Old employees, even tho they are experienced in the business's particular domain, aren't valued higher than a new hire.