I think Nordic etc. are resistant to telling people "if you want to use Wifi you must use FreeRTOS" or equivalent, so they push the two IC solution instead just so their Wifi stack is partitioned physically from the rest of your system.
It just pushes more integration headaches downstream to the customer, in addition to being inherently costlier. Espressif had the core right idea there, even if it's not the right decision for all designs.
