Try driving near a place with a lot of roads that are close together, like an airport. You’ll quickly see that snapping doesn’t really work, especially if you deviate from the route the GPS is trying to take you on.

I do this all the time and it works remarkably well. Amsterdam and the roads around it are pretty dense, up to 6 lanes each way in quite a few places with all kinds of flyovers and multi-lane exits.

At what speeds? I'm in NYC, similar dense road systems. At a reasonable speed, snapping still works because it knows where you came from. In stop stop stop go traffic combined with lane weaving and ramp merging I've found it is not hard to trick the gps into thinking you're on a parallel access road or unrelated ramp for a little while.

It's possible your highways are newer or less congested than ours?