As said above. If it was so great, why is it not being used anywhere but phones ? Because its not as fast as the other solutions for what they do.
That's like saying "If jet engines were so great, why was everyone using propeller engines in World war 2?" The answer is quite simply
Cost and development time. These things do not happen overnight, and transitions take a while. Your complaints about ARM are the equivalent of standing up in 1945 and saying "if jets are so good why aren't they everywhere?". Well they got quite popular in the 60s and 70s, and now, they're a mainstay in the aviation industry.
x86 took over the market at a time when computers were *heavily* memory constrained, and CISC was hugely advantageous for dealing with that. Since then, there has been tremendous inertia due to so many tools and so much software being developed for x86/64. But we've now reached a point with silicon where RISC vs CISC is entirely a moot debate, because these chips have more cache onboard than supercomputers had *ram* back in the day, and both designs have converged in practice (with minor differences). ARM also found a huge surge in popularity and development thanks to smartphones. It was also smart about dumping the 32 bit ISA which drastically simplified core designs and allowed them to adopt a very good 64 bit ISA (AArch64). It is now poised to penetrate upwards into the laptop and desktop market, with a modern ISA that has many familiar developers, with more coming onboard. At the same time, Intel, realizing their mistake when it came to smartphones, attempted to push low power x86/64 into the smartphone market, but utterly failed to penetrate.
Since that moment, the writing has been on the wall for ARM to turn around and push into Laptops, Desktops, and even the HPC market.
You can also turn around the question and ask yourself this:
If ARM was going to suck, why did Microsoft spend time writing Windows on ARM, and even building an emulator for legacy x86 stuff? Qualcomm would not have developed the 8cx, and started pushing it in a few laptops, if they didn't think there would be a market. Samsung's upcoming Galaxy Book S with 28 hours of battery life wouldn't be about to launch in a month, if ARM was considered "useless" and Amazon wouldn't be worked on an ARM-based server chip for AWS if they didn't think there was a market for it. Nvidia wouldn't have announced the roadmap for their Xavier and Orin Arm cores... that are pushing into new markets... Why has Adobe been quietly developing ARM versions of Photoshop, Illustrator, Publisher and Lightroom??. Why is Avid already working on ARM versions of Protools.
Similarly, Apple has been working on faster and faster ARM chips for some time, and has been testing the waters with scaling it up (A#x chips iPad) and actively cooling it (Apple TV) for quite some time. If you're reading between the lines, the Mac Pro appears to be apple's LAST professional x86/64 machine. By the time they are ready to update it again (5 years from now) they'll likely have an ARM HPC chip ready.
As for all this talk about "It can't do real work yet" -- when the 8cx laptops come out, and when Apple's arm MacBooks come out, we will be able to compare ARM vs x86/64 performance in a bunch of real world tasks, across 2 separate OSes (Windows ARM notebooks vs Windows x86 notebooks & Apple ARM notebooks vs Apple x86 notebooks), and will have plenty of data to understand whether ARM is ready for "real work" yet or not...
I can imagine some people who haven't been paying attention, or have been in denial about the Spec FP and Int numbers are going to be in for a heck of a shock when that happens...