The unnecessarily large apps probably use cross-platform tools that ship their runtime with each installation, losing out on Apple's optimizations or they have multiple ad tracking or 3rd party UI libraries.

I am not an expert in mobile dev by any means since I switched from web to native mobile development barely a year ago but when I was still resisting to learn the native way of doing things I was exploring the cross-platform solutions and libraries to "take advantage of my current skills", anything that goes beyond the demo todo list app quickly escalated in resource consumption and development complexity.

With these cross-platform tools, the moment you try to do something a little bit differently than everybody else, you find yourself stitching multiple 3rd party libraries together and these libraries add up to the binary size and loading times.