As the article say, the primary reason is the Cost. The second reason would be Ads.

I cancelled my Spotify recently because I didn't use it enough and didn't feel the cost was justified. I wish they had an intermediary plan : Listen ad-free+High Quality X hours per month for $Y. If you reach the limit you can upgrade to the full premium plan for this month.

If my bill was around $3-$5 per month, I would still subscribe.