The answer is money and fallowing. While the films of the Spielberg/Hanks collaborations were artistic and prestigious many just didn't make as much money and breakground as the Spielberg/Ford Indiana Jones movies. Sure the Raiders movies were flashier but they also took more chances and were more creative. Also which films created a fan base? Certainly not the Spielberg/Hanks films. They are one shot deals. And let's not forget that Hollywood is ruled by the box office and money. The Spielberg / Hanks collaborations may have gotten the awards, it is the Spielberg/ Ford collaborations that got the real prize that mattered to Hollywood.
I'm Truly a fan of both of the combinations. But the story of Bridge of Spies has way more depth than Indiana Jones. Next to that, the acting of Hanks is way better than the acting of Ford.... at that time. Its a complicated comparison. I Choose Spielberg/Hanks, because i like the stories of this duo more.