Qualcomm is seriously lagging Apple but so are Samsung and HiSilicon[0][1], they seem to be about the same performance. Android Authority [2] tried to explain why Apple is faster and their best argument (among a few) seems to be that Apple's silicon is just larger. Qualcomm could probably make larger chips if they get payed for it.
That's somewhat over-simplifying their argument - the long and the short of it though was that Qualcomm has different business interests in chip-making (ie, bulk, cheap, quick to produce) than Apple - so Qualcomm is extremely unlikely to ever match Apple.
Of course if Google did in-house SoC design and had Qualcomm as a manufacturer then of course they could do it, but that's so far no happened and at that point it's Google's chip practically speaking anyhow.
One of the other theories I've heard is that it's partly because 4 is an unlucky number in Chinese, which is a major market. Thus why so many SoC vendors pushed to 8 core chips instead of taking those extra transistors and spending them on an L3 cache instead, which would have helped real world performance far more than the extra 4 cores do.
Probably not very true, but it's a fun theory. More likely is it just looks better on the spec sheet to have more cores & ever higher burst-only frequencies rather than the things that would have more bang/buck on more real world workloads like an L3 cache would. It's why you ended up with ridiculous nonsense like the Helio X20 & X30 (10-core SoCs with only 2 good cores and 8 low power ones)
Those low power cores don't take up a vast amount of die area, but they substantially improve battery life. Apple seems wedded to the idea that 12 hours of screen-on time is sufficient, so they're happy to keep pushing for maximum performance; other manufacturers are willing to trade off a bit of performance for a lot more battery life.
2 low power cores help battery life as they can handle all the screen off and background activity. 8 low power cores is just stupid. That 10 core chip in practice will function like a 2+2 quad. The other 6 low powers will be doing nothing of value at all.
Samsung could make a faster chip, but they pretty much have to put a qcom chip in us phones due to the qcom tax. So having a s8 with wildly different preformance doesn't make sense. For example the exynos chips can do 4k60 but Samsung limits camera app to 4k30 to keep it in line with us phones.
[0] https://www.anandtech.com/show/11540/samsung-galaxy-s8-exyno...
[1] https://www.anandtech.com/show/11088/hisilicon-kirin-960-per...
[2] https://www.androidauthority.com/why-are-apples-chips-faster...