Pest Control--Mice--Not taking the bait!?!?!

[Jacobus Rex]

Hi, 

SFR in Minneapolis. Tenants have complained of mice, three different times over 5-6 years. I've had local well-known pest control company there three different times, at least. Still in the last year tenant complained of droppings. He wasn't afraid to go after them. He set lots of traps with peanut butter and cheese and the gel stuff such as the Tomcat brand. He caught one mouse. Still saw droppings. This person had very good hygiene. The house was clean. As in the past, these buggers wouldn't take that bait.
QUESTION:  How is it possible they wouldn't take the bait?  Consistently over years.  Once in the house why wouldn't they take the bait.   Frustrated.