Hydrogen and iodine make hydrogen iodide. Two molecules on the left, two on the right: the number of gas molecules does not change.
Squeezing the vessel multiplies every concentration by the same factor. The forward rate and the reverse rate rise by the same amount, so the balance stays where it was. The lines on the graph stay flat instead of stepping.
Only temperature, or adding one of the substances, moves it. Compare it with the other three and you can see that pressure matters only when the number of molecules changes.