I bought my licence back in late 2015.
There is no mention of there being a subscription, just an expiry on the download link. See image.
So, it would appear that no enough money has been rolling into the bank to sustain the original model.
I guess it's that age old problem. Build up your business based on good will, expand, forget the good will that got you to where you're now and concentrate on fleecing more money out of those who have remained loyal.
I knew things were going south when you started adding Avast to the download.
I will continue to use ccleaner, but I will never pay £1 to the cause.