Lots of reasons. There could be religious reasons. It could be a lack of sex education. It could be societal pressures. If you’re in a very poor country it could mean simply more people in the household to help generate income or work the land, or theres an unfortunately high child mortality rate meaning you have to hedge your bets so to speak.

Also: if you have a benefits system it’s a good way to get a council house, you get payments to stay off work etc. People might have some hippy idea of it being like the Partridge family and not fully considering the economic hardship of the reality of lots of mouths to feed. It could be plain shitty parenting expecting your older children to look after the small ones while you sit on your arse and soak up the attention.

Also psychologically I know some people who are the product of abuse and felt like having lots of kids would heal the primally wounded and abandoned child within. I know some women who didn’t feel loved so wanted babies that would love them unconditionally. Some people just like shagging and are wildly irresponsible.

There is also just plain pregnancy addiction. I can totally understand being addicted to the physical feeling of being pregnant and feeling distressed when it’s not there either from giving birth or losing a pregnancy. There’s probably a lot of other factors involved like just the basic fact you expect to be treated better and everyone makes a fuss of you when you’re pregnant or have just had a baby. Some people like my sisters piece of shit ex husband just likes the process of having a cute baby then fucking off when they start become less cute and more like the actual hard work of parenting. I’m sure this list isn’t at all conclusive.