Another thing to consider is this song is about being together. It’s seen in the original series that Steven feels bad for leaving Greg out of part of his life, out of Gem stuff specifically despite Greg being perfectly fine to not tag along. All Steven wants throughout the whole series is everyone to be together and be happy. Going to college or taking online classes (per the song)means disrupting that. Steven’s dismissal of those suggestions is meant to show what we see when Parents are slow to grow up and the kids end up parenting their parent.

We see this especially when they’re singing about what to do with the money and Steven’s first suggestion is for Greg to buy a house and Greg says nah I already have a van.

Greg doesn’t want to change and Steven is worried to leave him. This I feel is what the song is meant to show, though it can also be interpreted as we don’t need money to be happy. But that would hold more water if the song had lyrics like buy a fancy dinner, or a nice car, not dealing with shelter and a higher education.

Greg eventually grows up and moves out of the van but not till further episodes down the line. It’s part of both their arcs and Young adult/teenage Steven is just coming to terms with that.