Why? Because the only way to for a working professional to accumulate a "reasonable lifespan" of product knowledge is to anchor themselves to one company? That seems incredibly short-sighted thinking given the changing dynamics of the workplace from remote workers to an increasingly freelance economy where people can work for disparate organizations and still accumulate knowledge, skills and capabilities that you might still find valuable if you weren't looking at arbitrary numbers like how long a person has spent with the same company name in their email signature.

Is it a good way? Sure.

Is it the only worthwhile and relevant way? Mmmmmprobably not.