Why do makeup artists not use primer?

I'm curious, why do makeup artists sometimes choose to skip using primer? Could it be that they believe it's not necessary for achieving a flawless finish, or perhaps they have found that certain primers don't work well with their preferred products or skin types? Additionally, could it be that they prioritize other steps in their routine, such as skincare or foundation, and see primer as an optional extra? I'd love to hear more about the thought process behind this decision.