For the same reason a new law is required for elected officials. If an elected official is currently exempt from insider trading rules, and if the rationale is that the official doesn't actually hold "inside" information, and if it's necessary to change that, then it follows that the "tipping" clause must also be updated.

This could also depend on how a new law is written. If the law is explicit that information gained as an elected official is material/non-public, then existing tipping clauses may already account for this.

However, if this is not explicitly accounted for, it becomes an easily exploited loophole.

I'm still curious though - why is this potentially a constitutional issue?

Pretty sure that is not the case. It's members of a household. Grown children living elsewhere are not restricted.