Re: Good article
So, as was said, because he wanted to get his end away.
Nah. Henry was well aware of the distinction between sex and marriage, he didn't need to divorce or marry anyone to get his end away.
What he really wanted was a legitimate male heir, with the emphasis on "legitimate". (And hence, indirectly, also "male", since a female would always be of slightly suspect legitimacy - c.f. Mary and Elizabeth.)
It's easy to see people as motivated solely by selfishness and hedonism, but often there are excellent political reasons behind these stories. Henry VIII is one such.