Standard and expectation also increased and even thought I grew up with 2 siblings in 2 bedroom apartment in Poland today nobody would want that - or good luck finding a partner that want that. You would expect to have house or at least 3-4 bedroom apartment to raise 3 kids.

Today also probably you need 2 cars instead of 1 family car because your partner also have to work. You probably also need extra money for babysitter or kinder garden because again your partner is working and probably less likely your parents nearby to help since most young people had to move to big cities to get a job.

It also used to be that having a large family was a source of honor. Today, it makes people uncomfortable. They may even take a condescending view of those with many children. People have formed a strange association between having many children and poverty.

What you find is that the highest fertility in the developed consumerist world tends toward the poor and the rich. It's the middle class that has the fewest children. This makes sense through the lens of consumerism: the consumption of the rich is not constrained by having more children, while the poor can't consume all that much anyway, so having more children doesn't really change their buying power meaningfully where conspicuous consumption is concerned. It is the middle class (especially the upper middle class) that is anxiously keeping up with the Joneses and engaged in aggressive and petty consumerist competition. They have just enough to consume conspicuously, but not enough that they don't need to prioritize their spending. Consumerism simply prioritizes conspicuous consumption to the detriment of fecundity.