Less about physical space, more about propagation delays. The configurability of an FPGA doesn't come out of nowhere; it's a bunch of multiplexers and pass tran

Less about physical space, more about propagation delays. The configurability of an FPGA doesn't come out of nowhere; it's a bunch of multiplexers and pass transistors which route signals around and control how they're processed by CLBs, and those elements all add delay, limiting Fmax.