Theoretically, you could sacrifice full compatibility by implementing only the APIs used for Google, Facebook, YouTube, Reddit, Amazon etc. and have something much simpler. But that would still be a hard task because you are making a big compatibility hack for certain websites. Like the wine compatibility layer only for websites. Except that the websites could stop working at anytime and then you'll have to pile on more interfaces to keep up with them.

When evaluating software utility we often times forget that websites are software and don't attempt cost them in. Using them is a recurring cost in terms of complexity. They are definitely not free or even low cost.