The [Hunter Ranger's Whirlwind Attack feature][1] states:
> You can use your action to make **a melee attack** against any number of creatures within 5 feet of you, with a separate attack roll for each target.

It does not specify that the attack needs to me a melee weapon attack but only that it must be a melee attack. Does this mean that you would be able to cast a spell such as [*inflict wounds*][3] if you multi-classed into a class with this spell or if you took the Magic Initiate feat and chose to learn the [*shocking grasp*][4] spell? 

I am aware that Whirlwind Attack does not actually count as taking the Attack action; However, clearly you can make a melee weapon attack with this feature, an option that ordinarily would require the "Attack action". So why could you not also make a melee spell attack, an option that ordinarily would require the "Cast a Spell action"?

I would like answers to assume that the following ruling made in the [Sage Advice Compendium][2] is correct:
>  Whirlwind Attack is unusual, in that it’s a single attack with multiple attack rolls...

[1]: https://www.dndbeyond.com/classes/5-ranger#Hunter
[2]: https://media.wizards.com/2019/dnd/downloads/SA-Compendium.pdf
[3]: https://www.dndbeyond.com/spells/inflict-wounds
[4]: https://www.dndbeyond.com/spells/shocking-grasp