What it takes to build an app nowadays

I have just recently started working on an MVP. I have taken a few months learning a thing or two about the JavaScript ecosystem. Skipping to now , I am simply puzzled by how much modern app development actually revolves around the use of third party APIs .I am wondering wether I am missing something about this whole process.I often find myself having to deep dive into the docs of some API, rather than some spend this time actually learning about a new technology , which I find mildly(might switch to highly ,as the time passes) dissapointing. Is modern app development all about putting independently provided pieces together ?