> wealthy parents tend to be wealthy because they are more intelligent

Not "more intelligent", just "unusual in some way". People can be wealthier than average for all sorts of reasons unrelated to intelligence (as defined by IQ). Here's a sampling of them:

Being social and good at sales. Most successful real estate agents I've met don't strike me as particularly brilliant.

Working a boring job, living modestly, and investing in index funds for 20 years.

Winning the lottery (either literally, or by accidentally buying something cheaply that turned out to be worth a lot)

Marrying rich and divorcing.

Inheriting wealth.

Being a successful athlete or entertainer.