The diversity of everything came to my mind first. Test people are a more diverse lot (gender, training,… 
) compared to your average IT-educated dev folks.
The diversity of challenges. I love that there is no “one model fits all” - although it can be a curse - and you have to figure out what the stakeholder landscape is. Aligning with the business and making something that matters. I know, I am where I can change the landscape as a consultant, others might prefer tinkering with the same thing. 