MEV

Whoever orders transactions in a block can extract value from that ordering. Arbitrage between venues and timely liquidations are the benign forms. Sandwich attacks are the extractive form: a searcher observes a pending trade, buys ahead of it, lets the victim's trade move the price, and sells into it, with the victim absorbing the difference as slippage they never see itemized.

Ethereum's response was proposer-builder separation, which splits the roles of assembling a block and proposing it. The intent was to stop ordering power concentrating in validators. In practice it moved the concentration to a small number of specialist builders, and the ordering rents did not disappear.

The closest TradFi analogue is payment for order flow and front-running, with one crucial difference: front-running a client order is illegal in regulated markets and enforced against, while MEV is a permissionless, publicly observable business. That is why it is best treated as a structural feature rather than misconduct. Execution desks manage it with private order flow, commit-reveal schemes and batch auctions, none of which eliminate it, all of which change who captures it.