Apparently the CPU version wasn't what some folks expected, and found something better about the performance under thier circumstances that made GPU version better for thier system.
Probably number of Cameras using Deepstack, and Hardware resources.
That was written prior to DeepStack being included as an option in Blue Iris. Things are constantly changing. With the latest generation CPUs you can live without a dedicated GPU card, but with older CPUs, like a 6th generation, a GPU makes all the difference in the world when using DeepSack both in detection time and, as a result of faster detection times, better detection accuracy.
The problem is that it takes a GPU with 1000, or more, cuda cores to work really well. Between crypto mining, chip shortages and bots snatching up every card possible to make money re-selling them, the cost of cards is sky high right now. The old GTX970 I'm using is worth more now than when I bought it.
I bought it used ( probably from an Upgrading Crypto miner) for like...if memory serves me....about 3 years ago....for like $185? I'd have to try and find it on ebay purchases if its still around. found it.
I bought NVidia based on what Blue Iris recommended years ago. Until a couple of years ago BI couldn't use NVidia for hardware acceleration. Now it does HA and DeepStack without breaking a sweat.