Just a guess. Your car is new enough to receive over the air updates whether you subscribe or not. I have a lifetime subscription to Sirius/XM when I purchased my car in 2009. I would get frequent over the air updates and had to to logon to to reactivate my subscription during the early days of the car ownership. I haven't had to do anything in the last 10 years.
No updates for nearly two years, then two in 24 hours and nothing since?
Nope, not buying that explanation.