No idea why or how, but it might limit your search somewhat.
Speculatively I would attribute his attitude to contemporaneous British-inspired propaganda (and it’s not like he is likely to have experienced much of a decent sample on which to base his opinion - not that such considerations ever hampered the rest of his theorizing), but who knows?
[QUOTE=GorillaMan]
I don’t see why it’s all that surprising. He only died in 1939, so we’d still be within (for example) a 70-year copyright awarded to his estate.
[/QUOTE]
UK copyright. But in the U.S., all of his works published before 1923 are now in the public domain.