Why is it that ventura is not compatible with certain macbook pro models?

elizljeffery wrote:

Why is it that ventura is not compatible with certain macbook pro models?

Because some computers are too old having hardware not capable of running the newer technology operating system.

macOS Ventura is compatible with these computers - Apple Support

As Bob pointed out, technology advances. New versions are written to take advantage of new hardware. There will always be a point when older Macs can no longer support the latest version because they can't support it.