Why do jet engine fan blades have a twisted shape?
I don't think it's accurate to say that the desired thrust is the same along the entire blade. For a large turbofan blade like the one in your image, the outer part is designed to act more like a propeller (efficient for the bypass air) while the inner part is designed to act more like a compressor (efficient for the core). You're not incorrect in stating that the twist does help optimize the angle of attack with the speed of the section, but that's more about not breaking the speed of sound at the tip than keeping thrust constant along the blade.

For any specific engine, though, the blades are highly optimized based on an incredible amount of complex CFD and wind-tunnel analysis for which there is no simple or intuitive summary. The design of a turbofan blade is driven by several factors, mainly


aerodynamic efficiency,
structural efficiency,
noise,
temperature,
vibrations, and
bird-strike resistance.


All of these go into the resultant shape, but you're unlikely to find specifics that are non-proprietary to the manufacturer and available for anyone to analyze. The twist specifically is just another parameter in the extensive, complicated optimization.