Apparently, that wasn’t a normal boring route; it was way off course and erratic, so perhaps it was followed for that reason. I don’t know, but I’ll stay with a gut hunch it was tracked. With hundreds/thousands of satellites, who knows what they track.
By the time it became not boring it was too late to start following it with a satellite. Things don’t work like in the movies, if they had no reason for satellites to be taking pictures they don’t just suddenly have pictures anyway. The last time something interesting happened in the Indian Ocean Nixon was in the White House, it’s just not a spot to waste time taking and processing picture of.
With a finite number of satellites it’s quite easy to know what they track. And normal passenger jets on normal routes are NOT on that list.