several reasons but mainly due to economics. let me explain.
back 75yrs or so,ppl had larger families. they needed the extra help to run farms.with more and more automated production and machines,less ppl are needed to produce the same stuff. we are producing so fast that more is being put out than is used. hence prices have been adjusted and inflated to cover this.now there is less $$ for the average worker.they can not afford more children.sdo of course family size has gotten much smaller.

the average family has what 1 kid now? 25trs ago it was 1-3,25yrs before that it wasd a lot higher. the Amish still have the large familes and is the fastest growing population in America.not just the fastest growing white population.they still need the kids for help on those farms.

if you are an elite you don't need as many peasants supplying your needs. AI and machines have replaced the need for ppl.thios was predicted way before computers became a household item. was predicted before generations got lazy and spoiled.

At the moment you do see the world economies change from a consumerism mentallity.it is changing slowly.consumerism needs more pplp buyiing all the odd extra produced goods.as it is now, we throw more away than ppl use. this has led to high prices.