Hard problems are a lot more fun to solve. How do you attract top talent if you are only solving easy things?
Look at the sites that have succeeded the most and you'll see that they all solve basic problems, and that's resulted in most of them making tons of money. More specialized sites are more fascinating, but they attract fewer people and tend to be much less successful in absolute terms.
Is search not a hard problem?
YouTube solved the video codec Gordian knot, Google did the same with relevant search. Not easy problems, but they have huge benefits.
And, while the details are usually tricky, I find that Google's solutions to problems tend to always be brilliantly simple. Like their translate features: they figure out a basic problem and they solve it simply and often unexpectedly. Calling it a Gordion knot is actually the perfect description, yeah.
A hard problem is just a bunch of easy problems tangled up together.