Why a decrease in federal due with sale of primary & rental property in same year?

Hello,

 

I am running mock tax scenarios to help prepare for our married-joint 2024 filings as we sold our primary residence this year (owned 10+ years) and will be paying LTC gains on the profit.  We are also contemplating selling one of our long term rental properties this year and when I input projected sale ($200k) and profit ($100k) data, our "federal taxes due" amount drops by $10k.

 

My question is: how would our amount due decrease if there is a long term capital gain on the sale of the rental property?

 

Thank you TT Community.