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.

Older women may not produce that many eggs, if any at all. And each harvest costs multiple thousands, so it’s not all that clear cut.

To expand on what notimetorelax said, egg harvesting is a low risk but not a zero risk procedure which involves preparatory hormone injections, twilight sedation, and ultimately sticking a pretty fat needle into the ovaries. There's roughly a 1 in 1000 chance of serious complications for any woman that goes through it. If you're over 40 and your last round of harvesting only produced a handful of eggs cells and all of them with some kind of defect, repairing a damaged egg or zygote would be much less risky for the mother. What exactly the cost of a treatment based upon this discovery would be, I have no idea, but both processes are resource intensive.