Oda already gave a lame excuse about why WB did not go to help, wonder what excuse we get for Roger
Roger doesn't really need excuses. Roger died 1 year after the crew disbanded and Oden returned.
For Oden, he went to fight Kaido when he came back, but then accepted Orochi's and Kaido's trick deal of waiting 5 years for them to leave. So during that first year, and those 5 years of Oden dancing, there wouldn't be any crazy news coming from Wano such as "Oden died" or "Oden is danger", so Roger would have no reason to go help Oden during his last year alive, and besides, Roger was probably really sick and couldn't do much.
And there's of course the reason that not a lot of information comes out of Wano, especially back then, when even just finishing the first half of the Grand Line was impressive. So Roger would never get news of Wano in that year, while Whitebeard would only get news after Oden died, so we already know what his decision was.