I don't know the answer to the first question, except maybe what Sean said and/or that the legacy systems are integrated with other systems, workflows, etc. they use and it would be very expensive and possibly error-prone to upgrade them.

Whether it's wrong to take advantage of a company is a matter of opinion, but IMO, companies are inherently evil and profiteering and exploit anyone and everything they can, including you, and as such, they have more than enough money, so it's not wrong to take advantage of/cheat them.