For example, for me, it took a week of work to get going with Nordic Semiconductor Cortex M4 devices. Was totally unfamiliar with them.
This includes two-three days reading documentation, looking at the "simple" examples supposed to print "Hello World", but failing to do that because 5000-line-of-code logging library used to print that "hello world" requires so much understanding and configuration, including a massive file used to configure the color in which Hello World is supposed to be printed.
Finally after a few wasted days, ditching the "SDK" completely, just copypasting my usual STM32 linker scripts and startup code, modifying my existing GPIO helpers, etc., the thing was up and running in no time. Documentation quality is OK, examples are not. Peripheral design is exceptionally simple. Got UART and SPI working in matter of minutes. Even the RADIO peripheral was very simple to use on register level, and well documented.
In my opinion, writing bare metal with the available reference manuals / datasheets is always the easiest part. Most of the difference comes from the tools, libraries, SDKs, examples, etc. If you rely on them, their quality is of utmost importance. IMHO, the only sustainable choice is not to rely on those, at all.