I see nothing wrong with preferring to go to Europe after you've already run Boston more than once.
But, the Marathon, even apart from what happened this year, is a huge undertaking for the whole area, not just the city, as it goes through several smaller towns and cities. Here, we don't do regional. Every town is its own little fiefdom and this is one thing they all cooperate for. Yes, we do make money from this. And we love having it here! I stood and watched people run up Heartbreak Hill every year during my childhood, in my hometown of Newton. It's also spring vacation week here and Patriots' Day. There's a huge amount of tourism going on, in addition to the Marathon. Of course, prices will be up. I complain about the tourists overrunning my town for the Patriots' Day re-enactments, but it brings a huge amount of money here.
You could stay outside of the city, nearer to the start.... but, you'd need to have a car to do that.