Because without intelligent computers, the world we've built for ourselves would just... stop working. They have brought us medical advancements not possible 20 years ago. So we would pull the plug and kill many people. Not only that, but countries are competing against countries with their technology. So if America pulls the plug, everyone else is far more advanced and you have lost your military and political power. There is no "pulling the plug" unless the world is willing to pull the plug and willing to deal with what amounts to another dark age-- in which case, technology such as we see today is likely to develop again.
This tech is almost inevitable. We are creator beings. We want to make something that matches our intelligence-- and we always have. We've made pantheons of Gods to match and overcome us, we've made these autonomous beings in the stories we tell and in the dolls we played with when we were kids. The problem is that we don't know what machine intelligence may do when we let it out in the world. If they can learn the tasks we want them to learn, can they then learn how to learn a task we didn't assign them to? What kind of task would that be? How would we control it?
There may be no controlling it. But if we started focusing on this problem right now we may be able to figure it out. Instead, most everyone in AI is working to pump out as many "smart" things as possible, trying to develop better learning algorithms, get AI to become as human as possible, trying to make machines that behave like us but better, without paying attention to the future costs.
Maybe for the first time in human history we can learn without making the mistake.