LECUN: Why did it take so long? That’s just the way science works. It’s psychology. Before a set of techniques is adopted, people have to be convinced that it can work. These methods had a bad reputation of being finicky and requiring some black magic.
And the same is true of how much computing power to use -- you have to believe it's going to work.
Now that it's doubling every 3.5 months (on the largest projects), there are a lot of believers.