This is very simplistic and I would say there is more reason than only consumerism. People still might have kids they just have it less - they are happy to have only one kid because they fill fulfilled and also they cannot afford 2 or 3.

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.