This may not be a case of whoever booked this tour being clueless about Megadeth's drawing power though. It may have more to do with what venues the tour promoter has deals with. I think it's cheaper for them to book venues they have a contract with already even if the venue is too big and tickets don't sell good.
Still, it's better to see a band play a small or midsized venue that's packed rather than seeing them in a big arena playing in front of a half empty house.
3/20 - Dream Theater