My Wife and I Claim One Allowance Each; Why Do We Still Owe Money?

My wife and I file as married, filing jointly. We claim one allowance each and we each make $39k. Why on earth do we owe over $400 after filing our 2019 return? We have no other income and the only additional form we have is regarding $540 of student loan interest paid in 2019.

 

Why are we not seeing the appropriate amount of money withheld from our paychecks?

 

We got married in 2018 and saw a significant drop in our refund the next year. We'd both been used to getting refunds of over $1k when we were single but that first refund was less than $750. We don't understand why things have changed so much now that we're married and why it's so much worse in this second year. Everything our families told us before getting married was that we'd see even better refunds.

 

None of this makes sense and we cannot afford this.