HI
Does this make sense recall for a malfunction indicator lamp?
Note the Parts list
Pistons x 4
Rods
Head Gasket
Find the document at the below link
https://static.nhtsa.gov/odi/tsbs/2019/MC-10163888-9999.pdf
My question is what indicator lamp are they fixing by rebuilding the engine?
They're not fixing the indicator lamp, they're fixing the internal engine problem that caused it to illuminate.
Note the Parts list
Pistons x 4
Rods
Head Gasket
Those parts are the main components in the engine. If you've never seen models/ diagrams of 4-stroke engines before, you might consider looking at one: 
They basically messed up the guts of the engine. That's pretty impressive, since they've been making 4-stroke engines en masse since 1908. I can only imagine what else that's hidden within the car that will prematurely break.
@justin-shepherd By all accounts those are really terrible engines.
I had a feeling. GM has pretty much always made crappy small displacement engines. Compact cars and SUVs still aren't their forte.