Being rational, intelligent, and able to make good decisions sounds great. If you could wave a magic wand and grant these things, I'm sure many people would like to take advantage. In the absence of a magic wand, the journey can be unpleasant and fraught with peril. Making progress involves seriously examining your own life and dealing with all those problems you'd rather not confront. It can ruin your present social life and require you to find a new circle (as with recovering alcoholics recognizing the difference between friends and drinking buddies).

And there are plenty of failure modes. There's a stereotype that the youth who first discovers atheism becomes arrogant and quarrelsome. A little learning is a dangerous thing. There's an initial decline in effectiveness of reason before it catches up to (and eventually surpasses) good old common sense. No one likes a straw Vulcan.

I would heartily recommend Erasmus of Rotterdam's In Praise of Folly for a satiric look at the benefits of not-thinking and irrationality. Here's an excerpt which I think is fitting for the present discussion:

To these, as bearing great resemblance to them, may be added logicians and sophisters, fellows that talk as much by rote as a parrot; who shall run down a whole gossiping of old women, nay, silence the very noise of a belfry, with louder clappers than those of the steeple; and if their unappeasable clamorousness were their only fault it would admit of some excuse; but they are at the same time so fierce and quarrelsome, that they will wrangle bloodily for the least trifle, and be so over intent and eager, that they many times lose their game in the chase and fright away that truth they are hunting for. Yet self-conceit makes these nimble disputants such doughty champions, that armed with three or four close-linked syllogisms, they shall enter the lists with the greatest masters of reason, and not question the foiling of them in an irresistible way, nay, their obstinacy makes them so confident of their being in the right, that all the arguments in the world shall never convince them to the contrary.

It's much, much easier. Thinking clearly for most people ranges from hard to impossible. Worse, you might come to unpleasant or even dangerous conclusions. Much better to just go with the flow.

It's quite ironic, but people don't engage in not-thinking because they think not-thinking makes them happier. Pretty per definition, those people don't make there decision based by thinking.