Each individual or group will have a different answer to that question based on their personality and goals. Yes, they can go out and shake the world with their power, but there will be Consequences to those actions.
As you have alluded to, when gods fight, worlds tremble. While that is very much true, another viewpoint is that deities don't think in the same frames as us mere mortals. These inscrutable beings from our perspective make their plans with centuries or longer in time frames and considering multiple worlds, or even universes.
Even a deity of war, who may very much like the idea of a world plunged into a super-powered war and conflict may not want that because it may hamper the potential of future wars in the long distant future. Alternatively, those one man army types may not make a war sporting or bloody enough so it is in the deity's interest to make sure that they don't start making conflict.
In this case, I use the term as a general power level. How they come across their power may actually have an influence as to why they don't get involved.
A high priest or even a demigod may be bound by the tenets of their deity, and their rules. Being so high in power, and likely favour, means that they are likely more privy to their deity's immediate plans and desires then anyone else. These people are not dispatched to solve the world's problems per say -- they are sent out by their deity to remind the world of their power or to fix a problem that the deity cannot fix themselves. To flex or to fix, but always to the deity's will.
Archmages, both living and undead, may be more involved in their own experiments and pursuits then actually meddling in world affairs. Some have tried that, and it ended up that people started relying on them to solve their problems -- which took away too much research time. No, better to just sequester yourself and maybe claim dominion over a village so that they can tend to your immediate needs like food and clothing. Research is more important here -- and if it gets too crazy, retreat into your own demiplane.
The greatest warriors might be in the best position to stop these things had they not been rewarded with land and titles for saving the kingdom/world from some dragon, demon, or non-euclidean horror. That drops them not only into politics, but into defence of their realm. So long as the problem is not in their lands, it is difficult for them to deal with it directly.
Lastly, there are those that just do not want to get involved for their own reasons. So long as their little bubble of reality remains intact and unharmed, nothing else matters. Be it due to their powers, their past traumas, or a promise made, they are staying out of it for as long as possible.
Now we come to the mortals -- The powerful and the average. These are the people that will be the scouts and proxies for the powerful. They will be given the job to give things a nudge in the correct direction where they can to help matters. They will cut their teeth on the minions and the lesser challenges that are quite beneath the more powerful to deal with.
Besides, back in their day they had to do that stuff -- it's how they got strong in the first place.
The mortals are in fact the first line of attack by these living forces of nature in the world specifically because they are less likely to break something important, like a capital city or a mountain. They are also unlikely to know any actual plans outside of whatever issue they are hired/told to solve.
Of course, there are people that want to meddle and have the power to do so. Perhaps they do get involved and Things Happen. Perhaps they actually fight in locales that aren't the material world in a sort of "Let's step outside" manner of action. After all a demiplane, or layer of an outer plane may be less susceptible to catastrophe than the material world.
Conversely, they have fought in the world, it has suffered, and that is why there is a tenuous peace between those that have the power to break reality. Most don't recall that time, but for those that do it serves as a dire warning.
The upper echelons of the Magocracy could be mired in politics. A world shattering event might be supported by some and opposed by others. The Magocracy is in a fragile balance only maintained by the foreknowledge of mutually assured destruction should that balance be shattered. Taking a side on an issue means not just trying to deal with the issue, but also with those that take umbrage with you taking a stance.
Your leader has the unenviable position of being able to kick the most ass. As such, they are also needed to keep those under them in line. Imagine if they go out to stop the apocalypse, what kind of mayhem they'd return to? There might be a magocracy standing when they return.
Likewise, those looking to advance would not only be trying to advance but would also have power and resources tied up in their own defences. They may not have the ready resources to go save the world, even if they want to. Too much power is tied up in not getting ... deposed ... while too much money is tied up in acquiring said defences and their own studies.