OP here: Thank you everyone for your thoughtful replies. They are so helpful at this difficult time!
17:59: I am so sorry to hear this, and was shocked to read we had such a similar experience. They aren't even really giving the egg quality explanation as they said the eggs morphologically appeared excellent. Dr. Payson did say "maybe your eggs aren't tolerating ICSI as well anymore", for which there is literally 0 scientific evidence, and can't really be explained by a 75% fertilization rate of 16 eggs in June. I have looked at dozens of studies. One thing I have found as a potential explanation is a technical error of timing - either starting the process too soon after retrieval once eggs demonstrate MII, which can compromise cytoplasmic maturity (which isn't really observable like nuclear maturity of eggs is). Did they do an investigation or just said poor egg quality and that's it? The embryologist did say to us "we may have missed the fertilization window" when trying to explain what happened.
23:46: There have been many studies that show that the overstimming compromises egg quality argument is completely false. High stimulation can mean that egg quality is low (hence the need for high stimulation), but it does not cause it. I'm actually also on quite a low stim protocol - 200 Gonal F / 150 Menopur - so wouldn't fall into that category of overstimming anyhow. This article shows that the best IVF results across thousands of studies is when 18 - 20 eggs are retrieved.
https://www.sciencedaily.com/releases/2018/09/180904103259.htm#:~:text=Summary%3A,at%20in%20today's%20IVF%20treatments.
22:46: Yes, that is a great idea, thanks for that advice. I am going to ask for that. We are also going to ask for them to cover an additional cycle. They said of the other two retrievals that day, fertilization rate was normal, so that it likely isn't lab error. To which DH said 'If I take my car to the mechanic and they damage something, but didn't damage other cars that day, that doesn't mean the mechanic didn't do something wrong with my car".

There is lab error - contaminated culture that would affect all eggs that day - and there is technical / human error that may only occur once. If a lab technician drops a tray of embryos for one couple, that doesn't mean they will drop all embryos for that entire day!
00:43: I am very sorry to hear that. I think it is much more common for ICSI or conventional IVF to fail with a small number of eggs

. Of the 76% fertilization rate, we have good blastocyst conversion rates. Over the last two banking cycles, we have banked 9 blastocysts that are untested and frozen. For prior cycles, we had good blastocysts that were all abnormal, or failed fresh transfers, with one twin miscarriage.