Ummm. Do you realize how much amazing music has been written over the last 100 years by people who don't read music? Did Lennon / McCartney read music? Nope. I guess they had a shitty work ethic. :/
In case you missed it, films scores aren't always classical orchestral symphonies. Actually, over the last 4 decades they rarely are orchestral. A very quick example list:
Chariots of Fire and Blade Runner were both composed by a guy who was self taught. No symphony, almost entirely electronic.
The Andromeda Strain & Full Metal Jacket scores were an experiment in noise. Almost entirely electronic.
Marathon Man was hyper-minimal jazz. A bit of orchestra, very experimental for the time.
Solaris & Traffic were ambient masterpieces, scored by a former Chilli Peppers drummer who probably doesn't have much of a clue about scoring for orchestra. Some orchestra, very experimental, lots of since and world percussion.
Deadman was a bunch of Neil Young guitar feedback.
Amores perros, Babel, etc. were primarily simple Latin acoustic guitar based songs by Gustavo Santaolalla.
Fight Club was scored by a hip-hop / electronic duo The Dust Brothers.
Oh Brother Where Art Thou was scored by T Bone Burnett - a guy with a background in roots-rock and country music - who also probably doesn't have a damn clue how to score for an orchestra.
Yet all these scores were perfect for the films they were written for. Some of them won Grammy's, or had #1 hits, or sold millions of copies of the OST album. Some of them are for relatively unknown obscure films. Some of them are for hugely successful films. But ALL of these scores WORK. Which is the only thing that matters in the end.
Get your pretentious dick out of the orchestral asshole and you'll see a massive diversity of film scores over the last 100 years. By people that could / could not read music. By people who could / could not play an instrument well. By people from a wide variety of cultures, and from all different kinds of genres: classical, blues, country, ambient, noise, African, Cuban, folk, rock, rap, dance, and on and on and on.
Zimmer is just one of many on this list. He happens to come from pop music - that's his background. He likes synths, and soundscapes, and effects, and simple melodies, and simple chord progressions. That's his thing. It works. Get over it.