The Indianapolis Colts have had a good offensive line for years. While the offense hasn't been great for many previous seasons, the fault hasn't been the O-line. This year, even with a couple of key changes, the line is stout and efficient.
It helps, of course, that left guard Quenton Nelson is a future Hall of Fame player at left guard. Left tackle Bernhard Raimann is also fantastic, but it is right tackle Braden Smith who might be the most unsung of all those players. That is what happens when someone plays right tackle.
NFL teams want to spend tons on a left tackle because that position protects a quarterback's blind side, as most QBs are right-handed.