Everyone tries to do the same thing
These movies are so weird, plotwise, as everyone tries to do the same thing in them. The nazís, Indy and Brody were both after the same thing, essentially. Well, Indy wanted to save his father, but the father and Brody were after the grail, so in the end, Indy was also after the grail.
Why struggle so hard when everyone is going for the same thing anyway? Why not do what the 'bad guy' of the first movie did; wait for the other party to get the treasure, then figure out a way to get the treasure from that party. That way, you don't have to struggle, they can do the struggling.
I suppose it's a 'race to the goal' in a way, but everyone always ends up together at the end anyway, so what's the point..