It may not be because they disapprove of the product.
Landlords often finance their properties with bank mortgages. A bank mortgage almost always contains a clause requiring the property to be used lawfully.
Unfortunately, federal law still makes marijuana completely illegal. Therefore, a bank can call a loan and demand that a landlord immediately pay the entire loan amount if the landlord rents to a cannabis business. If the landlord cannot come up with the money, the bank can foreclose on the property.
Some landlords do not want to take that risk.
Right now, with the truce between the federal government and states where marijuana is legal, banks are not acting against landlords. However, that could change if federal law enforcement becomes a real threat.
This means that leasing property for a cannabis business may be harder than it is for other kinds of businesses and it may cost more because of the landlord’s risk.