Because almost none of the electronics you buy come with a replaceable battery, the second you buy something and use it on a regular basis it's destined to die and be thrown out within the next 4-8ish years due to the battery degrading and becoming increasingly more dangerous to keep around. Something that might be in perfect working condition and could be used for another 10 years has to be thrown out because of one single component.
I understand that batteries come in all shapes, sizes, capacities, yada yada, but imagine if we had standard rechargeable batteries like we have standard non-rechargeable batteries and things were built in a way where you could easily replace batteries like we could on phones a decade ago. You would double or triple the lifespan of a ton of things.