Why does exclusive order flow let two builders dominate 86% of Ethereum block production?

Private order flow agreements between wallets, apps, and a small number of builders give those builders a structural informational advantage that compounds over time. Beaverbuild and Titan Builder produced roughly 86% of Ethereum mainnet blocks during a two-week period in early 2025, and the Herfindahl-Hirschman Index for block building rose from around 0.2 in late 2023 to 0.35 by mid-2024. ePBS moves the builder-proposer auction on-chain but does not break the exclusive deal pipeline: a builder holding the majority of private flow still wins most auctions after the protocol change. BuilderNet is a voluntary countermeasure without on-chain enforcement, and as of January 2026 it produced only 25.5% of blocks. The feedback loop is self-reinforcing: only builders with high market share attract exclusive flow, and only those with exclusive flow consistently win.