The Sikh history provides at least one explanation for this. They're a very new group, formed around the 1600s. For a long time they lived in adverse conditions, at odds with local rulers, disadvantaged by numerical inferiority.
Given that monk culture is a form of specialization, similar to how a professional army is a specialization, and that specialization can't appear in adverse, numerically difficult situations, that could explain why Sikhs don't have monkhood, instead preferring rounded jack-of-all-trades social roles.
For an opposite extreme, there's The Kingdom of Tibet, which until Chinese occupation had 1/3 of its (male?) population in monastic life. That's extremely special; if only it had lasted.
Given that monk culture is a form of specialization, similar to how a professional army is a specialization, and that specialization can't appear in adverse, numerically difficult situations, that could explain why Sikhs don't have monkhood, instead preferring rounded jack-of-all-trades social roles.
For an opposite extreme, there's The Kingdom of Tibet, which until Chinese occupation had 1/3 of its (male?) population in monastic life. That's extremely special; if only it had lasted.