It maybe a stupid question, but I want to know the key reason of why RouterOS needs to shutdown by software first while other routers not, even routers with OPENWRT or other powerful firmware, we just unplug the power if we what to switch them off...
Yeah, sure... "nothing" happens apart from needing a reset when things go awry (usually if you poweroff/poweron too many times).
It doesn't matter the OS, OpenWRT and all its derivatives (DD-WRT, tomato, gargoyle, you name it...) or RouterOS, if you unplug power too many times you will end with NAND corruption sooner or later, probabilities rising exponentially depending on NAND activity.
You can unplug a router without problems, if you do it every now and then. Do it several times each day for some months and no matter if routeros or any other OpenWRT, will fail.