Read up on Schrems II. This policy is actually based on a court's decision not on a decision of politicians. Politicians actually tried to save data transfer with the "Privacy Shield".
"The CJEU ruled that the Privacy Shield does not provide adequate protection, and invalidated the agreement. The court also ruled that European data protection authorities must stop transfers of personal data made under the standard contractual clauses by companies, like Facebook, subject to overbroad surveillance. This decision has significant implications for U.S. Companies and for the U.S. Congress because it calls into question the adequacy of privacy protection in the United States."
"The CJEU ruled that the Privacy Shield does not provide adequate protection, and invalidated the agreement. The court also ruled that European data protection authorities must stop transfers of personal data made under the standard contractual clauses by companies, like Facebook, subject to overbroad surveillance. This decision has significant implications for U.S. Companies and for the U.S. Congress because it calls into question the adequacy of privacy protection in the United States."
from https://en.wikipedia.org/wiki/Max_Schrems