Why do you think birth rates are declining?

My grandpa (1915) had 13 siblings, my dad (1956) had 3 and I (2002) am an only child. This pattern seems to show up in statistics, why do you think this shows up? Personally I think it’s changing lifestyle, mg grandpa grew up on a farm where having lots of kids to help work the fields absorbed some of the cost of having them, my dad was in a small town and I was born in the city where life is expensive and there’s less room so tons of kids are kinda a liability. I think another factor is stress and lack of time, Americans work hard and don’t have time for relationships a lot of the time, another factor might be contraception becoming easier to access.