I mean we’re both dealing off anecdotal stuff anyway, but ‘average laptops’ usually means a laptop with Windows and that normally means someone owning that laptop who isn’t particularly discriminating about how they use it. You certainly can normally reset one of those to factory and clear it out and it will run a lot quicker.
They also tend to have moving parts. Cheaper laptops will have shittier fans in the side that get clogged with dirt. Often if you can open them up and properly clean them this will improve their speed as it’s down to dirt preventing the cooling working well, and bigger CPUs for larger computers tend to get big performance hits as they overheat.
And regarding Chromebooks not needing upgrades as often, again they’re very large comparatively and so all the components can be bigger and better designed. Our old iPad 2 was running fine in 2017 and still is according to the mates I gave it to. In fact I upgraded to an iPad 2017 because it was a little sluggish and was surprised how little speed increase I got from the new model.
But the iPad 2 is a 2011 piece of kit; in 2011 the iPhone 4S came out and I think you’d be hard pressed to anyone who would claim that iPhone is performing well. The size aspect makes a huge difference.
I think the reason new kit comes out is honestly that the old hardware does die in phones, precisely because it’s been designed to fit into such a small space, it is constantly heating and cooling (think of how often you pick up your phone and find it’s redhot due to mobile network use or whatever), so they will have to be replaced. Newer models will use better designed stuff to do things faster and closer to a full sized machine.