Considering that the Supreme Court was never really subject to the same disclosure laws that nearly every other public servant has, it was always my assumption that all nine justices were taking such gifts.
The fact we know this about Thomas and none of the others simply means that they haven’t investigated the others yet.
Even today, Supreme Court disclosures are not required by last in most cases (except when a related party has a pending case in front of the Supreme Court).
I don’t know that Congress has the stomach for the potential constitutional crisis that would occur should they try to really regulate the Supreme Court.
To be clear, none of what I wrote is well researched, it is what is percolating from the back of my head from conversations going back years.