People get hooked on this stuff before they even have biological urges to reproduce.
And it supplants the urge to reproduce.
Tech and entertainment are birth control.
How can you tell that isn't what's happened from looking at the rise of tech?
Sub-Saharan birthrates are starting to decline just as they're gaining access to smartphones.
All of the countries where women have fewer rights are also experiencing decline in birthrates. They have ~10-30% smartphone penetration.
"Having a child seems fun" is dopamine opportunity cost as much as a financial one. People have always been poorer, but they've never been so endlessly stimulated.
> I'm not in a position to have children because I can't afford them, so I won't. Now I have more time to fill, what's on TV?
Replace this with, "I'm bored. What's on TV / YouTube?" Everything else is unnecessary complication.
I don't think you can point to the rise of tech as a casual just because it's popular. If people aren't having children they'll do something else instead. To say what that is you need more evidence that what people are doing.