There are several factors that make Northern Colorado and Fort Collins specifically such a strong market for real estate sales and rentals.
We have great, diverse job base including a huge tech, healthcare, breweries and university for jobs.
We're consistently named as a top place to live attracting employers and workers to consider the move. Part of it is weather with 300 days of sunshine a year, part is low crime and part of it is great local culture.
We are a growing University town with a good number of students and more coming each semester.
There probably are a bunch of other reasons, but that's a few good ones.
I will also mention, since I track stats on rentals for my clients that we have seen a slight softening of the rental market (which is partly seasonal). This is NOT to say that the rental market is not still super strong, but it is not the crazy insane rental market we've seen recently.
For example, here are rents by week for single family homes in Fort Collins (all bedroom configurations).
Also, when we run our analysis numbers, we still recommend (and use) 3% for vacancy and strongly recommend investors start looking for tenants at least 60 days prior to your current lease expiring.