These content aggregation sites don't actually help in learning. The best way is still, IMO, to learn from an expert or experienced person.

I totally agree with you. There are lots of sites which are aggregating and curating content but expert teachers are less who can educate anyone properly.

But the main question is how to get experts and knowledge from them?

I disagree with you. With education content spread across various websites, there is a need for an aggregation and curation website. Yes, the content needs to be prepared by an expert, but the students can do self-learning.