What's up with recent pop songs stealing from older songs?

I can think of several ones that have recently been released that fall under this categorey: Sugar by Flo Rida, takes the Da Be De etc. from Eiffel 65, Right Round by Flo Rida takes it's chorus from the Dead or Alive song Spin Me Right Round, Stronger by Keane West has Harder Better Faster Longer by Daft Punk playing in the background, Live Your Life has the numa numa song in the background, the Miley Cyrus song Rockstar sounds exactly like Scotty Doesn't Know and another Miley Cyrus song See You Again sounds like Sungles at Night... What's up with this new wave of using old songs?