You know it used to be worth a lot more, and may be again someday, but it's uncertain. You suddenly get an offer that's higher than the current market, so you take it since you have no real confidence the market will be back to its former levels in the next decade. Yes it's a good offer for the moment, but there's still an element of fear/uncertainty driving the decision.

It's also potentially scary to Microsoft since they may have paid a price that's well above anything the market will ever see again.