How can old phones be slower while doing basic tasks?

Because to show an image, instead of using 1 library, they use 3. Because they just discovered the new trendy graphics library which needs a shader to put a rectangle on the screen. Because they must mine user data while the user is trying to use the phone (hello Google). Because although the OS does not allow more than one "app" to be active at a given time (hello Google), there must be a lot of "services " running to collect user data ( hello Google, hallo Facebook).

Apart from Apple's "battery lifetime optimization", a system having an actual history of use will always be a bit slower (or if badly optimized, a lot slower) than a new device.

Have you tried factory-resetting your old phone if that's an option for iPhones, to get more of an apple-to-apple comparison?

Lots of FUD here but the short answer is a combination of:

* Hardware does degrade a bit over time

* New OS versions add more features that eat up CPU cycles, but also add more abstractions to make developer’s lives easier but potentially be less performant. These features and abstractions are often also optimized for latest phones, since software and hardware design are so tightly integrated.

* Developers tend to optimize for newer hardware, since that’s the hardware they tend to have available

* Finally, there’s just been a huge amount of progress in iPhone hardware from the X to the 13.

Software aside, the storage (NAND flash) in the phone actually does wear out and get slower with use. Given how many writes modern software likes to make, this can add up.

But, critically, this wear doesn't just happen. It only occurs when the NAND is written to. It won't happen if software is effectively caching and combining writes.

A lot of what makes software snappy on phones is fixed function hardware, ie hardware acceleration. The hardware gets more specialized and the software gets heavier.

Follow the money. They profited by slowing down your old phone.

Maybe this is on purpose, but at a minimum why would they put effort into making an already sold phone keep up?

> Did developers become so lazy that they don‘t really optimize anymore?

It seems like this doesn’t really line up with the evidence that phones got faster.

Apple deliberately slowed down old models to force you to upgrade.

https://www.bbc.co.uk/news/technology-51413724

> A phone created this year should perform the basic tasks as well as in 5 years, shouldn‘t it?

I don’t see how comparing the performance of a two different phones in 2021 can say anything about comparing the performance of a single phone now and years ago.

The new phone just is faster. Compare https://browser.geekbench.com/v5/cpu/10853484 (about the best I could find for the iPhone X) with (about the worst I could find for the iPhone 13 Pro), and you’ll learn the newer one is almost twice as fast as the older one.