Sla’s change in velocity is 30 m/s, and hazel has the same change in velocity. which best explains why they would have different accelerations?

Because acceleration depends not only on the change in velocity.
It also depends on the time during which the change occurs.
The formula is

Acceleration = (change in velocity) divided by (time for the change) .

Maybe Sla changed his velocity in 3 seconds, but Hazel
took all morning to change hers.  In that case, even though
the amounts of change were equal, the times were different,
so the quotients of (change/time) were different.