That was true in the "early days" (basically the days of the Roman Republic). At that time, "Rome," (basically central Italy), was beset by Greek outposts (of so-called Magna Graecia) in southern Italy (as far north as modern Naples, at one time), Tarentum, and the Italian "boot." Also Carthaginian outposts in Lilybaem (Sicily), Caralis (Sardinia). And Carthage and its allies in North Africa weren't that far away. During the time of the Carthagian threat, a Roman Senator, Cato the Elder repeatedly exhorted his country to destroy Carthage: Carthago delenda est
By the end of the Second Punic War, Rome had neutralized the Carthaginian and Magna Graecia threats. They still had to worry about the balance of power in Greece itself, and whether the Macedonians, the Selucids, or the two in combination might threaten Italy from across the Adriatic. But four successful Macedonian wars (and one against the Selucids) took care of that threat.
Maybe there was a further threat from the Celts (Rome's ancient enemy) in Milan, and in Gaul. But Caesar's conquest of Gaul, and the earlier conquest of Spain and Milan had neutralized that threat.
By the time of the Caesars, Julius and Augustus, Rome had neutralized the immediate threats. It had no real need to expand further into Britain, Germany, or much beyond the shores of the eastern Mediterranean.