Today, top 3 block builders produce over 90% of blocks on Ethereum via MEV-boost auction. The block builder market's dynamics evolve rapidly and has significant impact on the development of private mempools, wallets/apps orderflow auctions, and censorship resistance topic. In this talk, we share an overview of why the top builders win the most market share, using orderflow composition and bidding behavioral data. We hope to highlight the centralizing risks and failures of current market design.