There's always some degree of "churn" in any competitive industry, and as long as the number of departing customers is about the same as the number of new customers, it's probably not worth the effort to find out why. OTOH if the airline is suddenly losing large numbers of loyal customers but not attracting new customers, it would point to a more significant issue and I assume they would want to figure out what had caused the change.
I let my paid Qantas Club membership lapse last year, after more than 20 years, and half-expected that someone might contact me to find out why. In my wilder fantasies I even imagined them offering me a discounted price to come back.
But all I got was a few emails extolling the glories of the QC which appeared to be aimed at "QFF but not QC member".