I can certainly understand why audiences may have wanted to get at least a bit more information on Aunt Becky, especially as D.J., Kimmy and Stephanie prepared for their massive triple wedding at the end of the season, with a lot of festivities and planning which would usually see a trusted aunt come around to help out.
We aren’t given any more details about why Becky hasn’t been around previously in the season, or why she doesn’t show up later.
And, we get no more mentions of her by the time Fuller House wraps on its final season.
But, I can also see why the producers chose to keep it simple.