I don't see a very big reason mentioned: You might not need it at all. Sure, the optimal age to freeze might be 19, but if 80% of women are done with children by age 30, why would you have every woman spend the equivalent of buying a small car on something they're overwhelmingly not going to need?
Waiting to get a good balance of "your eggs are still reasonably healthy" and "if you haven't had kids until now, it'll probably be a while still" is probably the reason behind the current advice.
Apparently the harvesting procedure typically (but not always?) involves general anesthesia. That alone is never entirely risk-free. In this context, the temporary loss of bodily autonomy could be particularly problematic. All that comes on top of the required hormone treatment. It's not a trivial procedure.
On the other hand, it may be a useful tool to resist expectations to become a mother until it becomes socially acceptable to say no. So it might be important even if the eggs are not getting used.
This is the best argument against early egg retrieval. If it were just a matter of money, the argument holds. However, the treatment involves pumping you with hormones that make you feel like crap the week before and after. Almost daily bloody draws are involved.
Then you add potential complications from anesthesia and the egg retrieval itself, and you have a net negative expected value.
The first time my wife underwent egg retrieval, the surgeon accidentally pierced her ovary. She has had pain on that ovary since.
There's no way it's a worthwhile investment to invest thousands of dollars and take on significant risk and discomfort just for a tool to "resist expectations." You should invest that in a therapist. Or moving to a different state.
> if 80% of women are done with children by age 30
Is this assumption based on anything? Not saying you're wrong, after all the majority of the world's population live in poor countries where people have children younger. But at least In my social circles it'd be more accurate to say 80%+ of women start having children at age 30 (or later) then are done with it. And I know multiple women who had their first child at 40+!
No, the number is made up, I'm saying that there's a point where the advice makes sense. Whether or not that's actually the case now is then a matter of statistics.