Buy art because you can
Save up and buy art because it enables you to participate in the culture of your time.
Buy art as a heirloom for your family.
Buy art for it's ability to cheer you up ( or otherwise make you think) at times in your life when nothing else makes sense.
Buy art so you can illustrate to your children that money is not the most important thing in life.
Buy art to impress your potential mates, their parents or your friends.
Buy art to support artists. They make our world so much more interesting and our darkest days so much more bearable.
Buy art because you like it.