While stock buybacks were catalyzed by "the adoption of SEC Rule 10b-18 in 1982," prior to which "companies avoided repurchasing shares because of the risks of violating the anti-manipulative provisions of the Securities Exchange Act of 1934," stock buybacks were commonplace going back to before the War [1].
[1] https://www.cfainstitute.org/-/media/documents/book/rf-lit-r... page 7
The difference was that they mainly took place in the form of tender offers back then rather than market repurchases.
I agree it should really be taxed at a similar level to dividends though.