1) I do like the service and use it all the time and 2) convenience.
I mostly drive my truck, which I just bought in August 2015. SiriusXM was free for 90 days. Before it expired, I received a "promo" deal in the mail and paid for a year or service at that time.
Likewise, I bought my car in June 2014. SiriusXM was free for 90 days and then I signed up for, I believe, a quarterly package. I, personally, have only driven my car twice in the last six months or so -- probably less than five times since I bought the truck. My girlfriend has a Jeep but she drives my car most of the time, so I keep that subscription active because she prefers the satellite radio over FM, Pandora/iTunes/etc. Otherwise, I would cancel service in the car.
I also have a package and receiver on my Harley. Due to the weather, I get to ride it perhaps half of the year. It's an inconvenience to call up and add it to my account in the spring and then remember to remove it as winter nears and the bike goes into the garage for months. Besides, we occasionally have nice days in the winter when I can ride and I want it to "just work".
Then, there's the Internet streaming service. I have the SiriusXM app on my iPhone (so I can play it via Bluetooth when in someone else's vehicle, etc.) and Roku and we have a "tabletop" receiver next to the bed. We often turn it on when going to bed, the girlfriend will listen to it while getting ready for work, etc.
In short, I do like the service. I'm probably paying them more than I should but I likely won't cancel it anytime soon. As I said above, though, I'd gladly pay them more for an "{ad|commercial}-free" version.