The reason why should be obvious. Because there is no reasonable way to maintain control over the data once it is sold. And no KYC requirement for buyers. The brokers probably really don't know (and may not care) who the buyer is.
This registry for data brokers is ineffective and meaningless.
Or from the user's point of view - once it's collected. It's not enough that Toyota (sadly I don't think they're unique) doesn't sell my car location data [1] - I don't want Toyota having that data either!
[1] https://www.tomsguide.com/news/toyota-exposed-car-location-d...