Not all places combine sick and PTO, that's why they differentiate them as "sick days"
I've worked places that gave x days PTO and y days for sick leave, though it's fucking stupid and prefer where I work now that just lumps the 2 together into one big time off pool
Where I work now is really weird as far as time off goes. I don't get a limited number of vacation days. But I do have a limited number of paid sick days.
Some places just want to be very clear that sick time is the same for every employee while PTO hours can vary based on seniority/merit etc. Most folks already understand that, but some people need it spelled out.