At some point, the goal is to standardize across backends, but the design work for that hasn't been done yet.

For getting started, most users want sane defaults with maybe one or two tweaks, but for complex applications, you really want access to the simpler pieces so you can build the event loop that best fits your application. Otherwise, you end up having to build your own event loop out on top of an existing one with a hodge podge of setTimeout, requestAnimationFrame, requestIdleCallback, timers, etc.