One of the issues is the inconsistency in defining generations. Some say Gen X is 65-76, and Y is 77 - 96 or 81-96 or 84-96 depending on your source. Gen Z is 97-??? and the Millennials label gets applied to Gen Y and/or a combination of Y & Z. --so it kind of depends what definition a study is using?
Cost of entry into driving seems like it ballooned in the 90s, and most younger people are in urban areas where driving oneself isn’t necessarily a priority. Most of the student cars in the parking lot at my high school in the 1990s were the country kids.
At some point though… driving becomes a true need for most people, and some discover the joy of it. I have been saying for some time that people under 45 are still a ripe ground for enthusiasts just don’t expect them to be into 64 Buicks (picked that as I happen to like them).