To learn and to make us use our brains. Philisophical questions usually arent as simple as yes or no and they actually require you to think and use your brain. Its important to excersice our brains so we can stay sharp and continue learning.
Because questions makes us thinks which develops or reasoning and logical abilities. We need philisophical questions because we need to be able to think for ourselfs and do our own reasoning.
To learn....why is it important to ask any question?