Actually, the higher the fat content, the LESS it froths. The frothiest is skim milk.

Because frothing is done with pressurized steam, the protein in the milk COOKS. Protein which cooks becomes more solid and so the bubbles stay = froth. Think of a raw egg when you first break it and then after frying. Any meat cooking is limp and floppy when raw, and more solid when cooked. Same with milk.

Since there is a less protein in any cream, there is mostly fat and it doesn't get firmer when cooked.