Schubert’s piano sonatas are something of a special case in music
history. Only a few of them, such as the G major “Fantasie-Sonata”,
were printed during his lifetime; the rest were published
posthumously, and it was only with the publication of Deutsch’s
systematic catalogue in the 20th century that they finally came to
light. For various reasons, they were long seen by musicians as minor
works. There’s one very telling story which seems plausible enough to
me: back in 1934, the great pianist Artur Schnabel ran into the
composer Sergei Rachmaninov at Abbey Road Studios in London. When
asked what he was doing there, he answered: “I’m recording the
Schubert sonatas.” Rachmaninov was a bit taken aback, and asked,
“Really? Did Schubert write sonatas too?” Now Rachmaninov was, of
course, an erudite, highly intelligent musician, no question about it
– it was just that at the time, so few people were aware of Schubert
as a composer of piano sonatas".
https://danielbarenboim.com/daniel-barenboim-records-complete-schubert-piano-sonatas-on-deutsche-grammophon-label/
I have heard a different version of this where Rachmaninoff was asked
during 1927 if he would program any of the piano sonatas during the
anniversary year 1928. I don't know if he ever played any in public.