In fairness, screw Lichtenstein (and Monaco). The entire country only exists to enable rich Europeans and uber-rich corporations to avoid paying taxes. It has more registered corporations than citizens, if that gives you any sense of the financial shennanigans the country is involved in.
San Marino has the unfortunate luck of being surrounded by Italy.
So, if you're planning a trip to Venice, you could spend a whole week without leaving the city. Maybe go to Padua, Vicenza or Verona.
Going to Florence? Same thing, and maybe visit Pisa or Siena.
There's a lot of Italy to explore.
Some war-torn countries are more popular than them.
Most likely because the war-torn countries make it into the International news... and therefor there will be people outside of Europe who are aware these countries EXIST.