As UX design as a field is maturing, so are the insights into UX positions. A UX designer was always able to grow into a senior UX designer, but other options weren't really available within the field. Mainly because "the field" didn't identify and shape more distinctive positions. You needed to move to positions like project management or product owner. Or stick to being a senior designer.
Helping clients and users with better solutions was never an issue. But what happens when you want to level up yourself?