Fans generally have a MTBF (Mean Time Before Failure or service life) of 50,000-150,000 hrs use.
Pumps generally have a MTBF of @ 50,000 hrs.
Pumps are expected (by the manufacturers/OEMs) to fail first.
Cpus have their own protective systems, used through the motherboard, one of which is the cpu_fan header. If this header detects a low/no rpm signal, the cpu can/will shutdown/refuse to boot to protect itself from possible thermal damage.
Because of this, manufacturers will stipulate the pump goes to the cpu_fan header and the fans/splitter to any other sys_fan header.
Which is next to useless. There will be no control of the pump by the cpu_fan header (pumps are almost always 3 pin DC, the cpu_fan header is only PWM) and the fans will then respond to case temps which never get above the 50's.
So almost everyone uses the fans on the cpu_fan header and puts the pump on the sys_fan header. Motherboard manufacturers clued into this and started putting aio_pump headers on motherboards which are generally not controlled but are full 12v and tach, so perfect for the use.
That way the pump is always powered and the fans then respond to cpu temps, ramping up/down as needed for the loads.