What if she has other grandkids that live near Springfield?
The situation you compared it too may not be at all comparable. You are citing the example of athletes that sign big contracts and use some of the money to lift their family out of poverty.
After posting, that's exactly what I thought. Dave's sister must still live in the DC area. Out of curiosity, I googled.
Lisa Grohl is Dave’s older sister. She resides in Sherman Oaks, CA. Lisa practiced music in her young years too, but according to Dave’s words, she was interested in other directions. From time to time Lisa is mentioned as a bass guitar player at Foo Fighters recordings.
https://familytron.com/dave-grohl/Maybe we're just assuming his mom lives in Virginia because of her name. Maybe she doesn't live here at all and actually lives in California. Maybe Dave is flying here for something else other than visiting his mom.
You're welcome for all the sleuth work.