> more activities that are simply more fun and rewarding than having children

Close but it’s not about fun, it’s about exploring the new possibilities. There’s simply no time for having kids when you just transition to a new way of life and you don’t know what to do. You maybe want to travel the world or build a house etc so you work more and spend more towards these. The next gen is having more kids.

Bulgaria used to be a prime example of population collapse but today has the highest birth rates in Europe(not just EU). The population will still shrink but as the dust settles people have certainty, know what to expect from life and can make a choice of having kids. Traveling the world can be just a phase in the early 20s, don’t have to grind as much for the basics, the definition of success isn’t getting rich through hard work so a simple and balanced life with kids becomes a feasible and desirable option.