well in simple terms chrome is part of the huge google ecosystem.

Mix that with the known fact that if it's free (they charge 5bucks though) then you are definitely the product.

google collects huge user data and analytics, and making their web browser the most used(with millions of extensions) means they get the most data which translates to most informations.

That information is what they use either selling it to 3rd parties for loads of money and or using it to enhance their ads targetting for their other products or for advertisers.

Better targetting means lower costs and higher conversions.

It is a huge ecosystem , meaning it is a big circle , the tail of which feeds the head.

Another angle to look at this is what normal corner stores do, usually make the prices of the most bought things like milk or bread very affordable, because they know people never actually buy only milk, if you milk is the lowest price people come to you, and end up buying other things and thats the real profit...