In all probabilities, any person who claims to have made "millions", and still running a "YouTube" channel is a scam.
And if you see ads inside/alongside the video, then the probability of his claims of "having made millions" being a scam increases many folds.
Just think about it. What do millionaires do with the money they've earned? Couple of options:
They continue trading to convert those millions into billions
They live a comfortable life in a mansion if they've earned a lot
Conduct some paid seminars on trading with a high entry fee
They start doing charity
A combination of the above four
In no case, will any successful trader ever reveal their secrets for free. Moreover, think about the threat on their lives by the not-so-good people, who may go after this person as he knows the key to turning hundreds into millions, and those millions into billions.
Why would a millionaire put hardwork in creating and uploading YouTube videos with ads, unless he wants some small bucks from ad income when he is making millions? The ad income in meager, and there is no charity or no free mentoring.
So never trust anyone's claims that he made millions and now tutoring for free. The only people who make such claims are the ones who just know how things work theoretically - like what technical analysis is, what candlestick patterns may indicate, what PE ratios are, etc. etc.
Can they use this "knowledge" to make profits "and teach the same" to others through YouTube videos - Highly Unlikely.
Take such videos only as information and knowledge sharing. Use the tips at your own risk, as it is your hard earned money.
In conclusion to answer your question - "Why would a stock trading millionaire need some extra money?", - It is because he is not really a millionaire!