Re: Why did it take them so long to start
They expend those millions looking for the craft so that they can determine what exactly brought the plane down. You can say pilot error was "most likely" but you can't know that's what brought it down.
There are plenty of instances in which pilot error was assumed to be the cause of a plan crash, only for the subsequent investigation to discover extremely dangerous flaws in the aircraft design, or in operating procedures, or flight operation manuals, or any number of other things.
The possibility that there are planes flying around with potentially fatal design flaws is why they keep looking until all options are exhausted.
Even if it turns out to be pilot error, the money wasn't wasted. They can then understand why the pilots made their mistakes and mitigate that in future with improved training.