Because, as I ALREADY EXPLAINED, the iGPU has pathetic performance even compared to a VERY LOW END discrete card per the TESTING I did on both my Intel AND my old AMD iGPUs.
Iris Pro is NOT going to be anywhere close to the performance of the Nvidia GTX 750 ti, much less the MID RANGE 9xx cards.
The top end Iris Pro iGPU *MIGHT* manage to match my AMD A10-5700 as it has about double the cores of the Intel I did testing on, but that's STILL a sad joke compared to any discrete GPU less than 5 years old.
Maybe your tests were not using the full iGPU?
Running JUST the miner software + Afterburner to monitor GPU status during the testing, yes the FULL iGPU capabilities were in use.
Such as they are.
The Block Erupter was a single-chip USB stick from an early generation, and has proven to be INFERIOR on performnace (though not on efficiency) to many GPUs.
It's also a money loser and has been for YEARS on anything SHA256.
I AM going to be curious to see what the POLARIS based (not Vega) iGPU designs out of AMD have for performance - and how it compares to discrete GPUs with the same core count and similar core clock.
I'm betting they STILL don't match up well, due to memory limitations, but should be a major improvement over the A10/A12 generation.
The GT 740 doesn't even count as an ENTRY LEVEL card any more, much less "low-mid range".
GTX 1030 blows it completely out of the water and the 1030 is BARELY classifiable as "entry level" by current standards since it does get matched on gaming performance by some iGPUs.
Yeah I know the Block Erupter is old. I jumped on the ASIC train pretty early back then. But for my personal mining equipment, I basically have multiple general purpose PC's with low to mid range GPU's plus a few VM's on Azure. All that combined, I can pull off about 1.5-2 KH/s. Every bit of hash power I can add helps which is why 100 H/s from an Iris Pro 580 would help quite a lot considering I'm not mining with high end GPU's. The best GPU I have is a GTX 660 Ti. But since I basically don't have to worry about electricity costs right now and I don't have to buy new mining hardware, just using the existing hardware I have is a pretty good deal.
Also, you might find out how good Polaris iGPU's are soon. The developers behind TurtleCoin are working on a GPU cryptonote miner for the Xbox One X which uses a Polaris iGPU that's roughly equivalent to an RX 580 though some benchmarks even put it closer to an RX 590 in terms of performance. I think they're expecting about 800-900 H/s for the GPU performance. If it turns out to be accurate, I'd bet a lot of miners will start buying Xbox One's because of how cheap they are in terms of performance compared to the current price of a lot of high end GPU's.