Why are there so many Omicron variants?

I have been looking into the pattern of SARS-COV2 variants across highly-vaccinated regions.

My question is, why are the other variants not present in greater proportions?

Birth Of The Omicron Family: BA.1, BA.2, BA.3. Each As Different As Alpha Is From Delta. William A. Haseltine Contributor

In the image above, the history of evolution, or phylogeny, of SARS-COV2 shows a clear separation of Omicron from the other variants. The current spread of Omicron in the United States may point to a pandemic of the vaccinated.

Image taken from Eric Topol Ground Truths Substack

What could explain the link between Omicron variants and Covid vaccination?

The basic structure of the SARS-COV2 virus is defined below. Spike protein is equivalent to the key that opens the lock of a cell to allow the virus to take over the protein-making machinery inside the cell.

There are 2 methods of viral entry using ACE-2 as the route – endosomal entry and cell surface entry using TMPRSS.