Well for me, If my players aren't playing in Ravenloft or Dark Sun (which if you're playing there, being a murderhobo causes entirely different problems), then it is actually hard to get away with being a murderhobo. I think of myself as a reactionary DM. I try to stay away from linear plots, beyond the setting and the adventure hook, I only write the villains and their motivations. Everything else is moved by the players.
My first question is, in a world such as the one you described how is it possible that the players could get away with abusing everyone around them for an extended period of time and still make it to high level? Outside of supernatural forces (fiends, undead, elementals,fey, monstrosities), living natural disasters (dragons,primordials, gods) even villains have to have tact. Even the most bloodthirsty bandit knows that he can't walk into town and kill the nobility. In any world that isn't ruled by savagery (see Dark sun) it shouldn't be a realistic option. I am not telling you or anyone else that their players can't accomplish whatever psychopathic deed that they have on the agenda that day, but when you do things like that the rest of the world takes notice. You become enemies of the state, bounties are placed on heads, law enforcement will come after player characters in force, and last but not least you start attracting unhinged doo gooders that resemble characters like Batman, Paladin Anderson (Hellsing), The Punisher (Marvel). As a Dm few things are more satisfying than having an innocent character who was brutalized by such a party turn into a psychotic revenge seeking malcontent.
Moving on to actual reasons why being a murderhobo is not only hard but stupid.
1) Image - Public opinion will be very low of the party if they are tolerated at all. They could very easily be forced out of town or have the local authorities attempt to lock them away after they commit some nonsensical murder.
2) Resources - If murderhobos suffer from an extremely negative public image (as they should) it will be hard to acquire resources in a traditional manner. If the towns won't permit you entry and the army is looking for you it becomes difficult to find food and water especially if the party isn't proficient at living off the land. Even other criminals such as the Zhentarim will shun outright murderers, you will be forced to associate with increasingly disreputable individuals as your infamy spreads.
3) Birds of a feather - Picking up off the 2nd point. In order to acquire goods, magic items, food etc, the party will be forced to deal with depraved and corrupt societies, that is if they don't go full banditry and start pillaging towns. The danger with associating with these kind of groups or creatures is that you aren't one of them and you don't know if they will turn on you and try to enslave you or whatever (happens a lot in the underdark, see drow, neogi, mindflayers, duergar).
4) Heroes of the Realm - If your campaign isn't full of sheep that are powerless in the face of the player characters, then there should be highly competent and dangerous Npcs somewhere in the setting. If the player characters continue their murdering psychotic ways and somehow avoid dying a dogs death in the wilderness, execution or life imprisonment, then paladins, clerics, and good aligned adventurers should start to pursue them, be it for revenge, acclaim, or whatever reason you need to justify some smiting.
5)Running afoul of greater evil - If somehow these players haven't died yet I'm questioning the Dm at this point, or maybe it's a villain campaign now, or maybe they are just as tenacious as they are psychotic. The types of personalities that lend themselves to becoming murderhobos are on average pretty arrogant and combative. These players are unlikely to be respectful to others and why should they, they are the bandit kings and queens of this world, robbing, killing, and pillaging as they please. But eventually if the DM is so inclined they could come across an evil that dwarfs their own, it may be a lich, it may be a dragon, a demon or devil but regardless if the players take their usual positions with this creature it should have dire consequences.
6) Betrayal - Last but not least arguably the most likely end to murderhobos, betrayal from within the party. Greed and murder as primary driving forces don't lead to a cohesive unit. I've seen it happen before, players start coveting the shiny things that one or another of them has and it culminates in theft or murder. Or it could be party members butting heads over who is the "leader" of the band of psychopaths, these kind of players don't lend themselves well to being second fiddle.
There might be more reasons but yeah.....murderhoboing is not sustainable.
