I was excited to see that Small Town Security was on the Roku app. However, there is only one episode available out of all three seasons. Why?
When companies like Roku license content to make available, the content owner is in complete control over which episodes/seasons they will allow. It's possible they want to gauge the demand for their content so they only release one episode. If there's demand for more, they will probably raise their price for additional episodes. Roku can only stream what the content owner will allow.
Try watching Small Town Security on the free Pluto TV channel. (https://channelstore.roku.com/details/0719d122fc30b9f282fa106a903ab1d6/pluto-tv-its-free-tv)
They have three seasons available.