Two (sorry three, sorry four, five) main villains
Microsoft's ever upward processing power requirements encouraging users to dump otherwise viable computers. Desktop and laptop makers for selling machines with substandard components that fail prematurely (power supply fans, motherboard caps*). Cellphone networks for offering "free" phone upgrades. Phone, camera makers for specifying otherwise identical power cube and batteries that are incompatible between models, let alone between brands.
Small changes, practical in most of the above could save a vast amount of waste (as per EU ruling on phone chargers).
* This is particularly maddening given that forty year old hifi components still work perfectly.