Why do chlorinated silanes have lower boiling points than their methane analogs?

The boiling points of the chlorinated silanes and methanes are given below:


$$\begin{array}{ccc}
\hline
\text{Species} & \text{Boiling point (X = Si) / }\mathrm{^\circ C} & \text{Boiling point (X = C) / }\mathrm{^\circ C} \\
\hline
\ce{XH3Cl} & -30.4 & -24.2 \\
\ce{XH2Cl2} & 8 & 39.6 \\
\ce{XHCl3} & 31.8 & 69.2 \\
\ce{XCl4} & 57.6 & 76.7 \\
\hline
\end{array}$$


The chlorosilanes are expected to have larger dipole moments and stronger dispersion forces. Why do the silanes instead have lower boiling points than the methanes?


