GPUs have always been squarely in the "get stuff to consumers ASAP" camp, rather than NASA-like engineering that can withstand cosmic rays and such.
I also presume an EM simulation would be able to spot it, but prior to rowhammer it is also possible no-one ever thought to check for it (or more likely that they'd check the simulation with random or typical data inputs, not a hitherto-unthought-of attack vector, but that doesn't explain more modern hardware).
This is a huge theme for vulnerabilities. I almost said "modern" but looking back I've seen the cycle (disregard attacks as strictly hypothetical. Get caught unprepared when somebody publishes something making it practical) happen more than a few times.
(personally I think all RAM in all devices should be ECC)
News would latch on to "Hacks say all computers without ECC RAM are vulnerable and should not be purchased for their insecurity. Manufacturers like Dell, Asus, Acer, ... are selling products that help hackers steal your information." "DefCon Hackers thank Nvidia for making their jobs easier ..."
Such statements would be refreshed during / after each security conference. There are over 12 conferences a year, about once a month these would be brought back into the public as a reminder. Public might stop purchasing from those manufacturers or choose the secure products to create the change.
It's more of a tragedy-of-the-commons problem. Consumers don't know what they don't know and manufacturers need to be competitive with respect to each other. Without some kind of oversight (industry standards bodies or goverment regulation), or a level of shaming that breaks through to consumers (or e.g. class action lawsuits that impact manufacturers), no individual has any incentive to change.
RAM that doesn't behave like RAM is not RAM. It's defective. ECC is merely an attempt at fixing something that shouldn't've made it to the market in the first place. AFAIK there is a RH variant that manages to flip bits undetectably even with ECC RAM.
Single Error Correction, Double Error Detection, Tripple Error Chaos.
It should be considered unethical to sell machines with non-ECC memory in any real volume.
I'm not versed in silicon fabrication to know if theres ameliorations involved past what hit the press near 20 years ago now. But, while deep diving modern DRAM for an idea, its shocking how small a change is needed to corrupt a Bit in DRAM.
It was known as "pattern sensitivity" in the industry for decades, basically ever since the beginning, and considered a blocking defect. Here's a random article from 1989 (don't know why first page is missing, but look at the references): http://web.eecs.umich.edu/~mazum/PAPERS-MAZUM/patternsensiti...
Then some bastards like these came along...
https://research.ece.cmu.edu/safari/thesis/skhan_jobtalk_sli...
...and essentially said "who cares, let someone else be responsible for the imperfections while we can sell more crap", leading to the current mess we're in.
The flash memory industry took a similar dark turn decades ago.
Nothing is perfect, everything has its failure conditions. The question is where do you choose to place the bar? Do you want your component to work at 60, 80, or 100C? Do you want it to work in high radiation environments? Do you want it to withstand pathological access patterns?
So in other words, there isnt a sufficent market for GPUs at double the $/GB RAM but are resilient to rowhammer attacks to justify manufacturing them.
In the datasheet.
The positive part of the original rowhammer report was that it gave us a new tool to validate memory (it caused failures much faster than other validation methods).