Why is raising Kaspa's blocks-per-second rate technically challenging?

Raising the blocks-per-second (BPS) rate forces a proportional increase in the number of blocks the difficulty windows must track, and that creates a complexity problem. Window size equals window length multiplied by BPS, so doubling the block rate while keeping the same time window doubles the number of blocks every node must process for each difficulty calculation. Shrinking the windows to compensate would hurt security. This tension — efficiency constraints on one side and security requirements on the other — is why the source concludes that finding a better way to represent a window is required before BPS can be raised further.