What is the reason for low fertility prediction?
Well it's a simplification. Better education also correlates with lower fertility.
And yes, I'm not showing causation. But anti-conception does require some basic money and education.
Worldwide experience has been that increasingly developed nations have lower average fecundity. There are various likely reasons but the correlation seems to be quite robust. In most countries it seems that the causal link was from development to fertility. It is arguable that China reversed the causation, politically limiting fecundity.
This is a uniquely human dynamic. Pretty much every other species in the world drives its population to its Malthusian limit.
If you are in the US you may not appreciate how heavy the tax burden is in Europe. It varies by country but its normally something like: 30% payroll tax paid by employer. 30% income tax paid by you. 20% sales tax paid by you. Then, very expensive housing due to the high population densities and limited room to expand.
Additionally in Europe, many parents want their children to be educated in English, however the language of instruction is usually the local language. This is partly why the migrant stream into the Anglosphere is so high. The alternative are private international schools, which are hideously expensive.
Housing in a second-tier Polish city is more expensive than Chicago!
https://www.otodom.pl/oferta/klimatyczny-apartament-balkon-w...
https://www.zillow.com/homedetails/5345-S-Ellis-Ave-H2-Chica...