I'm not sure what country you live in, but in the US,
Regan isn't ultra-trendy, based upon the popularity statistics. It entered the top thousand for the first time in 1974, fell off again in 1982, never having gotten higher than #650, then entered the top thousand again in 1991, but has never gotten higher than #389. I could not prove this, but I think that "The Exorcist" caused
Regan to become more popular and less popular at the same time. 1974 was the year after "The Exorcist" was released, so I think that's the reason it entered the top thousand that year. On the other hand, it's never gotten higher than #389, and is currently at #878, and given its close similarity to
Megan, which was indeed quite trendy and popular in the 80s and 90s, I really think that "The Exorcist" is the reason it hasn't seen much higher numbers.