Too Little tax withheld though on w4 with 0 dependents listed

My wife and I file Married jointly. On my W4 & G4 I claim zero dependents/allowances, and pay additional $100 Fed & $50 State in taxes. My wife started new job in 2020, and we did the same for her W4 & G4 forms but without the additional money payout. So that's 0 dependents /allowances for here as well. The reason for this is because I have a side self employment job where I get a 1099-NEC (no taxes withheld), and before this new job with my wife we would owe until we itemized. But I knew this  extra additional money from her would really put us over the top, and I'm want to avoid owing taxes. The problem is when she got her W2, only approx. 2% of federal taxes was taken for the year. So that's 2% (590+ dollars) of about 30k for the year. How is that possible, if she filed Married jointly, but zero on dependents and other adjustments? any Idea?

For state (Georgia) about 6.5% was taken for the year. My goal is to have the max amt taken.

Help! 🙂