Your smile didn't matter
If you worked on the line, we cared about your productivity, not your smile or approach to the work. You could walk in downcast, walk out defeated and get a raise if your productivity was good.
Your attitude is now what's on offer, it's what you sell. When you pass by those big office buildings and watch the young junior executives sneaking into work with a grimace on their face, it's tempting to tell them to save everyone time and just go home.
The emotional labor of engaging with the work and increasing the energy in the room is precisely what you sell. So sell it.