To be fair, I think the same thing is true of individuals, and it's not necessarily a bad thing. Often times the grass is greener on the other side. Granted, it's industry dependent, but if you are in tech then there are countless green pastures to pick from. From a company's perspective, they know they don't want to pay someone significantly more for the same position, so they figure they won't lose much by waiting for employees to leave and hire a fresh new employees for roughly the same wages as the preview ones. It also means any potential baggage created due to office politics and or bad attitudes work themselves out to some respect.
Unless one is an outright wizard at what they do, which is rare, what should make anyone think a company needs to keep them around? We are all replaceable. Companies should only hire internally if it makes sense. The fact is that 99% of us are just adequate in the eyes of our employers, and if they play their cards right, they have more to gain by hiring new team members than ones they know they aren't that enamored with.
Unless one is an outright wizard at what they do, which is rare, what should make anyone think a company needs to keep them around? We are all replaceable. Companies should only hire internally if it makes sense. The fact is that 99% of us are just adequate in the eyes of our employers, and if they play their cards right, they have more to gain by hiring new team members than ones they know they aren't that enamored with.