Question

why is it that evaporation causes cooling, but boiling causes heating

Answer 1

Evaporation is a surface phenomenon in which surface molecules take heat from surrounding to move into vapour phase. Therefore, it causes cooling.
Boiling on the other hand is a bulk phenomenon. When a liquid is heated, a stage is reached when the molecules of liquid acquire enough energy to pass into vapour phase. Since, the entire liquid is heated; boiling causes heating.