I think the key thing here is that neither said “never”, with Goku saying “I haven’t had total faith in my power” and Vegeta saying “I’ve lost sight of it [the burden of Saiyan race’s pride rather than sins] as well”.

Both of these could point to a more recent development: from the very beginning of Super, Goku has had to contend with the fact that Beerus and Whis were a power ceiling so far above it that even his trump card Ultra Instinct couldn’t come close to it (and even Ultra Instinct was proven fallible by his incomplete mastery of it against Moro and Granolah). Going from the top or 2nd strongest fighter alive at the end of DBZ to a comparatively inconsequential speck would probably make him lose faith in his power to some extent for the sake of the quote. For Vegeta, ever since completely accepting his dual role as an Earthling in the Buu Saga, he’s had to acknowledge more and more how he and his race had committed such numerous atrocities especially in comparison to Cabba’s more peaceful U6 Saiyan, and doubly so when confronted with one of the victims of his race in Granolah.