From my perspective, another factor of the declining interest in ballroom seem to be outcome from key technological advancements that have contributed and shaped the on-demand trend we see in US culture.
Over only a few decades people have moved from TV to Cable TV to streaming. Phones have went from devices to connect voices, to sending messages, to being high-powered CPUs connected to the world. Radio has evolved from analog to digital and had carved out a space in the digital streaming world as well. Newspapers have had to adopt an online streaming presence in order to survive. Even movies, have had to shorten box office releases and move to streaming partnerships to capitalize on public interest before it wanes on the new release.
We pause a show, short video, skip commercials, communicate with each other's via cell phone with minimal regard to schedule because the recipient will respond quickly or when it's convenient for them. We can earn diplomas/degrees 100% online or in some sort of hybrid arrangement. Even the rise in food home delivery services versus sit down restaurant dining (spurred by COVID) continues to move the masses toward the values of on-demand eating and quick/instant gratification.
Ballroom is a journey that can take years of in-person commitment to become competent, and so much longer if you wish to be considered good. The nature of this beautiful dance discipline is ultimately one that must be realized in-person with others on a fairly frequent basis. It is a discipline that is best learned in-person rather than in watching videos online. It's also a partner dance which requires coordination of schedules with an instructor or a partner in order to practice, learn, or just engage.
Ballroom education has a model that is almost the antithesis of the direction our society seems to be headed in my opinion. Our society seems to be moving into a more self-directed way of consuming entertainment/hobbies/doing daily life, and away from one which requires regular coordination of time/location with an instructor or partner and in a particular location.
Admittedly, earnest efforts are being made to increase social media/digital presence by DanceSport organizations and studios, while dance teachers are increasing the offerings of learning opportunities online. Students are taking lessons from their dance instructors at a distance and meeting up in person periodically for lessons. All noteworthy adaptations to a changing world. But, it seems as if ballroom comes to fruition best when people are in-person, dancing together. (It is a partner dance after all.)
Not withstanding the concept that ballroom incorporates multiple dances; each having their own characterized nuances and a broad variety of timing combinations which require a longer time investment to learn.
I think that ballroom requires a significant investment of time and physical presence and that seems to go against the emerging trends of how people in mass spend their time that I see in our current culture.
[And this long exposition is not to minimize the expense/cost of ballroom as a factor of declining google searches. I do believe cost is still a significant factor in the decline as well - and I can postulate on that one too.

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