Harvesting eggs can be a huge strain both physically, emotionally and financially. And if you're older, and thus have elevated risk, you might get just a one or a few eggs per harvest.

Now factor in that the success rate of eggs turning into viable embryos that can be transferred back into the mother can be low. Even if you harvest say 10 eggs, a good catch, you may very well end up with just 1-2 viable embryos from those 10 eggs. And that's before considering trisomy as discussed here.

The final kicker is that harvesting takes time. You might well only be able to harvest a few times per year. And success rate drops quickly once you're past 38 or so.