Why do Android devices slow down over time?

[Mooserman15]

My 3.5 year old tablet just isn't what it used to be. It is now a little slow. Why does this happen? And will a factory reset fix this?

 

[PapaGary]

A factory reset cured my Moto X 2013.

YMMV

 

[sydneycooper1979]

It can certainly help. That's a pretty long time in the life of an Android tablet. That's awesome!

 

[Silver Soul]

A factory reset will have it running like a champ!
They don't slow down overtime but there are several reasons as to why the UI might be sluggish
-Too many apps running in the background
-Cache partition is too big or you are low on space
-NOT ENUFF RAMMM
-No trim (which is rare)
Maybe try and install Greenify and reboot it every once in a while!

 

[Mooserman15]

A factory reset will have it running like a champ!
They don't slow down overtime but there are several reasons as to why the UI might be sluggish
-Too many apps running in the background
-Cache partition is too big or you are low on space
-NOT ENUFF RAMMM
-No trim (which is rare)
Maybe try and install Greenify and reboot it every once in a while!

Too many apps in the background: Not a problem for me. I have about 0 in the background.
Cleared cache partition yesterday, 2.8 GB of storage left.
My device only has 800mb of usable Ram, but RAM usage is actually BETTER than when I got the tablet.
What's Trim?
I'll look into Greenify. I reboot it about once a month, but an off schedule reboot gives no improvement.

Please explain what Trim is. I think it may be my problem.