The 14th Amendment came out post US Civil War, 1866. International travel was slow and limited. Today, a pregnant woman from anywhere in the world can get on a plane, fly to the US and give birth to the child in the US. That child, being born in the US, is a US citizen. The parent or parents are not US citizens. So a problem and dilemma is created on what the government should do with the parents (non-citizens) and the baby (a US citizen under current law).
Look at this situation from another prospective: Let's say an American couple, 10th generation Texans, people that bleed red, white and blue, become pregnant. They take a trip to China and the woman goes into labor and has the baby early. Does this make the baby Chinese? Do the parents get to stay in China for as long as they want?