Hey, welcome to the future. Isn't it awesome that you have a phone in your pocket that is also a pocket computer? We can read and write emails on our phones, visit websites, watch videos, and since smartphones usually come with a calculator app, they are also pocket calculators. Aren't smartphones awesome little devices? Yes, but there's a lot holding them back.
I've never owned an Apple phone, so I can't speak about those as I don't have any experience with them. I'm gonna be talking about Android phones and smartphones in general.
Random new apps
Whenever my Android phone receives an update, it also automatically installs a bunch of apps and random games with it, which I then have to uninstall or disable manually. Smartphones are nice but this stops them from being as great as they could be. Stop installing / downloading random stuff to my phone, please.
Slow and bloated
For the slow part, this isn't completely Google / the Android developers' fault, part of it is that, because the size is so small, you can't really fit cooling in a smartphone (no room for fans, heatsink etc.), you have to slow the hardware down a lot and/or limit how much power it uses so that it doesn't overheat and so it doesn't drain the battery in minutes. Part of it is about making the battery last a decent amount of time, and about preventing overheating. Laptops also have this issue, but to a lesser extent.
Now, the bloated part, this is absolutely Google's fault. The phones already have hardware limitations due to size and battery life, They don't need to be slowed down even further by constantly sending data to Google and the storage being taken up by shovelware apps. I can't / haven't tested this, but I bet the performance and battery life would noticeably increase if you removed / disabled all the code that handles the telemetry.
Apple smartphones: arguably worse
I changed my mind, I'm gonna talk about Apple phones. They cost too much, they are impossible to repair (to be fair, the vast majority of Android smartphones also aren't designed with reparability in mind,) and they have proprietary connectors. Did I mention the cost? Oh yeah, I almost forgot, both of them get updates that intentionally slow them down, to force you to upgrade your otherwise perfectly good phone.
I don't care if other sites have talked about all this thousands of times before, it feels good to rant sometimes.