They where popular way before microservices, only less dynamic. Mostly from an operational perspective they give a single entry point which can be better secure

They where popular way before microservices, only less dynamic. Mostly from an operational perspective they give a single entry point which can be better secured and monitored. It also allows to easily decouple unstable backends from your user so even though functionality is broken (404), the user experience doesn't have to suffer (serve stale cache, respond with a proper branded error page which helps the user forward (instead of a cryptic app specific error page).