alt Hacker NewsI 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.