Long cables add parasitic capacitance to the $\text{I}^2\text{C}$ bus, increasing the RC rise time constant ($\tau = R_{pull-up} \times C_{bus}$). Reducing the pull-up resistor decreases rise time, keeping signals within the valid logic-level timing windows. However, too-small resistors increase current draw. Active $\text{I}^2\text{C}$ bus extenders are used for very long runs.