If you read the history, you will read that Sarah couldn't conceive a baby. People don't want kids now, but in the past times, people wanted children.
When a things begins, you don't know the future. We need to trust in the Lord. The Lord had a great plan for Abraham and our lives.
27 This is the account of Terah’s family line.
Terah became the father of Abram, Nahor and Haran. And Haran became the father of Lot. 28 While his father Terah was still alive, Haran died in Ur of the Chaldeans, in the land of his birth. 29 Abram and Nahor both married. The name of Abram’s wife was Sarai, and the name of Nahor’s wife was Milkah; she was the daughter of Haran, the father of both Milkah and Iskah. 30 Now Sarai was childless because she was not able to conceive.31 Terah took his son Abram, his grandson Lot son of Haran, and his daughter-in-law Sarai, the wife of his son Abram, and together they set out from Ur of the Chaldeans to go to Canaan. But when they came to Harran, they settled there.
32 Terah lived 205 years, and he died in Harran.