Actually they extended the borders of the Empire whenever and wherever practical. It took a lot of farmland to feed the citizens on Eternal City. I agree with your point that they didn’t have the technology at the time because they didn’t need it. My original point was that if someone HAD made it back such a need would have immediately materialized. In which case, I have no doubt that Roman minds would have been up to the task of developing seagoing vessels.
Worth noting that the Spanish and French and the English and the Scots and the Scandinavians and the Portuguese all had ships suitable for traveling in the Atlantic. The Italians and Greeks and Turks are generally believed to not have such ships.
Colon, raised in Italy, sailed French and Spanish ships. Cabot, raised in Italy, sailed English and Spanish ships (and I think Portuguese ships as well)
By 1531 several nations had ships capable of sailing completely around the globe. Magellan, raised in warm climates, did it first. (Magelheis = MacWallace ~ He was from Galicia, as were the various Carvajals in the early voyages)