I spent so much time trying to get the SDK working for NRF52 that I genuinely just gave up and redesigned our whole product to use an ESP32 instead of the NRF plus other uC.
I think that is genuinely the reason espressif is eating everyone's lunch. All the old players in the IC business have such inexcusably bad SDKs that the acceptably designed and documented ESP-IDF framework just makes the most sense to use. Why would I spend six weeks fighting with Nordic SDKs with their weird system-wide installation when ESP-IDF can be set up in five minutes isolated to your user directory?
Seriously, it takes longer to find the correct Nordic SDK installer than it does to git clone, idf.py install, ./export.sh
And Nordic's weird documentation web portal is just egregiously bad. Espressif puts it in a static HTML page with a selector for the framework version. It's simple, elegant, and fast.
I did like using the NRF52 once it was finally behaving, but the ESP is just so easy.
I've found old SDK actually not that bad. Documentation is not great, but sources are available and it's just mostly C code with some hairy macros, but it's manageable. After few weeks I became quite proficient. I don't like their suggested approach "copy&paste example you like and tinker it", I never do that, so I had to untangle their Makefiles, I had to research their defines (app_config.h, what's a monstrosity), I had to write my own linker scripts, but in the end I have my application under control and it's all standard gcc toolchain, no fancy stuff.