In the case of Kracow, there wasn’t much farther to go, but there also wasn’t a great mandate to do it. Hadrian almost abandoned Dacia (was talked out of it) which had been conquered by Trajan, and which conquest had resulted in a huge haul of treasure that marked the economic pinnacle of the Empire. That second RE map link is pretty interesting in that it shows the four divisions of the Empire (done by Diocletian) as well as a couple of other “Hadrian’s Wall” which were constructed in Central Europe where no natural boundaries (such as the Rhine and Danube) existed. Despite his fabulous popularity in his time, Hadrian was ultimately a disaster for the Empire.
Wasn’t the walls on the border with Germania not really walls, but barriers that would force anybody coming across to be funneled to specific locations where large garrisons were located? I thought I read that somewhere that since Roma couldn’t cover the whole border they built this barriers, so they could allocate the Army’s resources better.