After thirty years of babysitting those same reefers on semi trucks I can tell you they need that satellite link because those units can go down at any time without warning. Mostly it's just small things like relays and solenoid valves but they are still not cooling or heating.
M. Nix
This is one of those things where our intuition is often poor because of the scale. It may seem like these things break down "all the time" but it's just because the system's requirement is 100% reliability, and the sheer number of components eats away at the MTBF of the aggregate system.
In college I worked as the house manager for the theater. We had a large amount of marquee lighting in the atrium, perhaps 200 bulbs. It seemed there was always a burned-out bulb, no matter how frequently we put in a maintenance work order. I was puzzled until I did the math: if the life of a bulb is 1000 hours, and they burn 5 hours a night, you are statistically losing a bulb
every night.
Similarly, an enterprise-grade hard disk drive may last 100,000 hours. In a datacenter with 100,000 drives, you are statistically losing a drive
every hour.