I find it always interesting that the Romans never reached modern Czechia or slovakia, even though they invaded Britain or went so far in the middle east.
Might be because of land travel in those days. I wonder how besides the large scale geography like mountains, the smaller scale and biotopes also affected it. Open farmland or steppes are different to travel than dense forests or cliffs. Even today, trade by land is still more constrained than by water, if you look at large container ships vs trains, and where most GDP is concentrated. Thomas Pueyol makes some nice twitter threads about this, how geography has shaped history. Of course simplified and with a chosen narrative, but something that the typical "great man theory of history" doesn't do.
I would guess because the whole region is surrounded by mountain ranges which must have been impassable "jungle". E.g. the Ore Mountains in the north were only settled after 1000 AD and mostly because of various "silver rushes". I guess the Bohemian forest to the west was similar harsh, no large rivers like the Rhine to transport troops on, and the whole area probably a scary, dark and "barbarian" wilderness like Germania north-east of the Rhine. Just speculating though :)
Oh, but they did reach those lands under Marcus Aurelius and indeed occupied them. Prior to his death, he intended to create two new provinces, Marcomannia and Sarmatia. There was even a Roman expedition that reached the Baltic in modern day Poland. (In the case of Poland, it would’ve been a terrible idea to try to conquer those lands, not least of all because they are situated on the indefensible Northern European Plain.)
Danube, which runs through Slovakia's capital, was Roman Empire's border.