Why Doesn't the USB Fit in the Slot?

Shouldn't all keyboard USBs be standard to fit in the towers of any computers?

So what's up here with this e-machines keyboard not being able to fit into this Dell 1100?

There's only one slot that a purple USB prong from the keyboard could go into -- this hole that is also helpfully coloured purple here on the back of the tower:

 

Yet it won't fit.

Now, why won't it fit?

If you look closely -- and it may not be visible in this camera photo -- the USB prong has a not only tines like a fork, but a kind of wedge that has to fit into a slot, inside.

And that doesn't match, as there is no slot inside the purple USB hole on the tower.

Hmmm. So I could cast around and see if I can find a used keyboard that goes with this Dell 1100 (used). Or get a wireless keyboard? I have a feeling those will break down a lot.