"Preserving the advantages of compact block relay is often cited as one reason for trying to keep mempool and relay policy consistent between nodes—the more the mempools of nodes differ, the less effective compact blocks will be at minimizing bandwidth and latency."
Knots makes it hard to keep mempools similar by inconsistently refusing to forward transactions. Makes efficient block propagation harder and stale blocks more frequent, costing miners money with no benefit to the netwrk, reducing security and lowering the value of Bitcoin
Footnotes