Until you join a FAANG you simply cannot imagine the complexity of the systems and how much has not been automated and how much there is to build.

I've been in Amazon for close to a decade, and I constantly think "I can't believe X hasn't been automated in the 30 years that Amazon has existed and is still done on Excel".

Most engineers will work on new features for at least half of the year, and I personally work on brand new projects or at least features constantly.