He really isn't, he just gave up after one too many failed attempts to usurp Megatron and decided to try and wait things out. He never truly was loyal.
Why does Bumblebee look sad after the cybermatter (that stuff he fell into) brought his past self back? He KILLED Megatron (temporarily, but still); that’s something to be proud of.
It’s a joke, because they have such a like. “Oh no he dead” look, instead of what they had in the show witch is genuine sadness(I know it’s a show but they executed it so well)
Can you make the burns family and transformers heatwave transformers chase and transformers green bulldozer and transformers blaze reacts to Cody can sing 🎤
At the end, it was a father/son moment as I imagine Bumblebee sees Optimus as a father figure. I hope this clears some things up if people were confused.