Maybe a stupid question from someone that is ranked "guru" in this forum, but;
Why is it needed to upgrade the firmware everytime the ROS is upgraded?

I only use Mikrotik products, I only upgrade with the winbox manual upgrade tool.

But I always need to do both. First upgrade ROS, reboot, log in again and upgrade the firmware followed by yet again a reboot.

What is the firmware actually needed for? And what does the latest versions bring each time?

And why can't the upgrade process not be a 'one action' thing? Upgrade the ROS should also upgrade the firmware... ?

I was a bit surprised I couldn't find any info in the manual about the reason why firmware should always be updated (ROS yes, that's clear) and what it actually does do on a ROS running product.

Good point. Looking forward to see the answer.

IMHO firmware is devices' abstraction layer for OS so it could be called "device drivers package" for particular platform.
I have written OS not ROS as MT boards could run not only ROS but other systems.

You don't have to upgrade RouterBOOT every time. 90% of RouterBOOT versions have no benefit for most people, they just add support for some new model.

The other 10% of changes are usually related to NAND, Etherboot and file system.

What's new in 3.18:

*) fixed boot from non-2-power partition count;

What's new in 3.17:

*) fixed boot from nand on yaffs (broken in 3.11);

What's new in 3.16:

*) ar9344: fix etherboot problems on CRS125 (probably other boards
as well);

What's new in 3.15:

*) qca9550: fix etherboot at 100Mbit/s speed (broken in v3.14);

What's new in 3.14:

*) button: add caps function to reset button;

What's new in 3.13:

*) setup menu: added 1 minute inactivity timeout;