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(original image by Wikimedia Commons user San Jose)
If you look at a topographic map of Europe, the reason should be self-evident: the easiest land route from northern/western Europe passes through the gap between the Alps and the Carpathians. Hungary sits in the middle of that gap; historic Hungary occupied effectively all of it.
This same geography remains an important factor in modern times: there are far more roads and railroads passing through that gap, typically by way of Budapest, than go over the Carpathians.