I would tell you that it is their age. And maybe the late season. Mine turn red after their on the plant for an extended time and it is getting to the end of the season.
I am still growing bell peppers in my garage, but they are still green and young. I plan to leave them on the plant and see if they age to red......I believe this is also the case of the hot peppers also....

I THINK the best solution is to plant seeds EARLIER indoors, and threby extend your growing season. Some hot peppers are very long season (especially for my short 90 day growing season.) Most peppers make good container plants.
just my 2 pesos worth,
Bruce

We start our pepers under grow lites mar 17 & in the ground last week of may grow green to yel. & green to red