But that doesn't really get to the heart of why crypto consumes so much electricity. It's true that every time a transaction is made it gets propagated throughout the network. However, these transactions only take up a little bit of data since they only really have to include information like the sender address, receiver address, amount sent, and other values. It’s like downloading a file online: if you’re streaming a movie, you don’t think about how much electricity your router is using. (For perspective, the Bitcoin blockchain, the full list of every transaction ever sent, is around 330 GB.)
Mining specifically is where most of the energy is used up. Without going into too much technical detail, when Bitcoin was originally drawn up it was decided that a reasonable method to verify transactions on the network would be to essentially run a number guessing game. If a correct guess is made then (a) the recent transactions would all be verified and (b) the miner would receive the transaction fees from all the transactions they verified (along with newly generated currency as a bonus).1 When this happens, it is said that a new block has been found and the block is added to the blockchain. It was made like this because it was believed to make Bitcoin resistant to attacks: anyone who wanted to verify fake transactions would need to have more computing power than the entire rest of the network. Therefore, it’s clear why mining causes so much electricity to be used up: more computing power means more capacity to guess numbers, and more guesses means more money.