I completely agree. While the idea is SUPER exciting to have someone with this amount of talent draw your character or something for you, spamming his comments with "could you draw this character?" would overwhelm him, and he just doesn't have the free time to do EVERYONE'S request.
It's obviously this fan was a special case. If you want him to draw something for you, consider maybe asking if he's open to commissions instead of asking for free? That way, you can get what you want, and you'll be supporting him in a big way. But if he's not open to commissions, then respect his choice, and simply enjoy the amazing work he does now.