App size can be measured in many ways like download size, install size, binary size, thinned size. I wrote about the most important ones here: https://docs.emergetools.com/docs/what-is-app-size
(I do understand that source code isn't what ships in the binary, but for the sake argument let's say they're 1:1 in size.)
Yelp, for example, is what you might call a "straightforward CRUD app" (to Yelp engineers, I know it's probably legit complicated and hard), and that is 292MB on the App Store.
It's probably to do with how the framework handles lifecycle management and combining static assets like text and image with business logic that lives in Controllers.
These are code. Swift is a safe language with more runtime checks than other "zero-abstraction" languages. It also support "value" semantics and can deploy monomorphization for generics (although no guarantee). All these means you can have functions with slightly different view models duplicated many times throughout the binary.
Not to mention the language itself need to generate a lot of retain / releases for refcounting purpose (the blog post also pointed this out).
All in all, Swift as a language is not particularly optimized for small binary sizes, and there are a lot of trade-offs made to improve the usability rather than binary size. That has been said, there can be more opportunities exploited (and right now not) to reduce the binary size from compiler side.
Also, the Uber app has a LOT more features than you would expect at a glance, due to extensive customization of the experience (i.e. feature flagging) along many vectors, and so it wouldn't surprise me at all if this ends up adding to a lot of code.
Edit: Linked post from sibling commenter bhupy outlines this in detail.
> The choice of Swift as our primary programming language, our fast-paced development environment and feature additions, layered software and its dependencies, and statically linked platform libraries result in large app binaries
but can somebody familiar with iOS development explain what makes app bundles so big? Actual CPU instructions or config can't contribute this significantly. The entire Bible is about 4.5mb. If you're writing an app by yourself you almost certainly didn't write that much text in the source code. A sibling comment links to https://news.ycombinator.com/item?id=25376346 which says that they have a lot of screens but even something like "PayTM (15+ screens)" is still just textual source code and config that I don't follow how it gets beyond kilobytes. The App Store places them at 309mb, so ~68 bibles.
I understand when games are large because they typically ship with images and videos included in the binary for game assets. But for a normal application where does the size come from?
Is it dependencies? (And how did _they_ get so big?) That weird intro video they have on the loading screen? Are they shipping bitmaps of the cities they have markets in?