Why do Android phones become slower?

Person buys a phone, it's not got massive amounts of storage because person is not rich. On the box it says the phone has 64GB of storage (we could call that RAM, but it's not like a computers RAM as it's persistent). Person turns on the phone, and it says 'Hi, I need to update all the provided apps.", The thing is, the provided apps, are in ROM, and do not impact storage (other than for their data), but the updated version from the App/Play Store is now stored on the main storage, reducing that 64GB the phone came with before you've even had a chance to use the phone. ROM is also faster than the storage, not by much but it all adds up. Apps in ROM are quicker than in storage. When apps are 'sleeping' their run states are swapped out to storage, if storage is low, then the phone constantly has to make decisions on what old run states or temporary data needs to be purged first to make space for the apps run state to be saved. If a sleeping apps run state is purged, then when you click on it's icon again, it has to start up afresh, which is slower. All these things add up to delays. Then there's the constant indexing of your photos, videos and messages, the more stuff to index, the bigger the database, the more time and CPU cycles it takes to maintain it.

Basically, it's phone death by 1000 cuts.

What I do on any new phone or factory reset is NOT update any app I never intend to use, and/or disable it if I can. I also regularly purge older photos and videos (after having backed them up to another medium first).

However, none of this will stop newer apps just being more complex, and eventually your phone can no longer keep up. Phone app developers rarely optimise their apps for slower hardware, as the 2-year phone upgrade behaviour is now so strong in most users.

Apps are a big part of it. You can quit WhatsApp or Discord all you like but they're still running in background.

A lot of apps are hackily built. Google is punishing this, but let's face it, you'll still use Messenger or Slack nontheless even if they ranked terribly on the Play Store.

Battery and system updates do matter. Android Lollipop basically made one of my phones unuseable. But you can try and uninstall everything and see the effects.

Also Samsung phones seem to deteriorate really fast for some reason. Most of my mid range ones became unuseable after 2-3 years.

Primarily because developer cycles are more expensive than cpu cycles and secundairy because the owner pays for the hardware but ultimately because of actual deterioration of ram and storage.

I noticed that: 1. Android phones run a little bit faster after restoring to factory settings and """NOT""" installing apps updates and system updates. Of course they will be obsoleted, but the phone probably will run faster. Hypothesis: [Are apps and system updates too heavy for phones?] 2. Sometimes phones run faster after battery replacement. Hypothesis: [Are phones becoming slower because they do CPU underclocking/undervolting to work with degraded battery?]

IMHO it's security updates and therefore unavoidable.

Why do I say that? IMHO it boils down to attack surface and counter measures. Any strategy an opponent is using to get your information is going to require energy and or time to fight off. Voilà.

Check your battery