Why were the Spartans not allowed to trade or travel?

A Spartans first vacation was to be a warrior, anything else would be bad to the other Spartans.

Spartan laws discouraged anything that would distract citizens from their disciplined military life. Sparta did not welcome visitors from other cities, and did not allow their citizens to travel. The Spartans were not interested in other ways of life and did not want to bring new ideas to their polis. Today, we use spartan as an adjective to describe someone who leads a rigorously disciplined life that includes few comforts or luxuries