Answer is very simple, they overcharge the local company with a huge comission.
They are sucking bloods of local suppliers! You can buy tours way cheaper if you buy directly from suppliers, for sure.

There were no fewer crowds, pick up and drop off, or any other perks with the tickets we bought from GetYourGuide. Just hugely inflated prices. I have no problem admitting when I've been duped in order to save someone else from the same fate. The tickets I purchased from GYG cost approximately twice as much as what I would have paid if I'd purchased them directly from the tour companies. Please don't be duped like me!

Paguei um preço justo para 2 adultos crianças não pagam o meu tem 12

I think you pay the price for the advantages you have wirh a tour such as skip line, pick up and drop off at the hotel, a guide... If you read everything that's included in the tour, you are going to find the answer. I paid the price and my family and I had a great time.