Because you have style="position:absolute; top:150px;"
applied to the image inside the footer. And there is nothing in the footer other than that.
Do this, to see that footer image is loading but is not visible due to positioning.
style="position:absolute; top:50px; left:100px"
or do this
style="position:fixed; bottom:0; left:40%;"
You need to remove absolute positioning and let the footer fall where it should, then apply relative positioning or absolute one if required.
A comment: bad bad HTML/CSS programming.
But as an exercise,
first create Container, Header, Content and Footer.
Fill them with data. Do not apply CSS yet, get to know their static positions first.
Then, move things around with position and floating.
This is not how seasoned web designer work, but it's a start.