Microsoft didn't NEED to buy the domain, they could have patched their code to handle the issue. Clearly, they did a cost benefit and decided it was worth it to buy the domain to plug a hole they created.
Another poster used the stocks analogy but I think the real estate one is more appropriate. Someone who bought land a long time ago that is now desirable to another party can has no obligation to sell at all (let's not bring eminent domain into this). Let's say instead of corp.com this was land next to Microsoft Campus in Redmond. Why shouldn't someone ask for as much as they can get for their land?
If they patch their code, they still have to get people to update. I know companies still running Windows XP. If you think people outside of the tech industry update their systems regularly, you're in for a rude awakening. My uncle's company still runs a DOS app written in 1984.
Another poster used the stocks analogy but I think the real estate one is more appropriate. Someone who bought land a long time ago that is now desirable to another party can has no obligation to sell at all (let's not bring eminent domain into this). Let's say instead of corp.com this was land next to Microsoft Campus in Redmond. Why shouldn't someone ask for as much as they can get for their land?