They know their needed maintenance times and can handle them better. Meanwhile my main game Destiny 2 has every patch maintenance that almost always gets extended by 2h roughly due to “unforseen issues” or so.
At this point Bungie became a meme for that within the community.
Blizzard on the other hand may have rough launch days in case of queues… But at least in almost all cases players can at least attempt to log in, without the game being not accessible at all.