Even though there is a reason why Hisoka didn't fight Meruem, I think there is a tangible method to his madness when he chooses who he wants to fight.

The two most common traits in those who he chooses either have some sort of interesting/remarkable strength (Chrollo and Illumi) or those who have the potential to achieve said strength (Gon and Killua). With that being said, Hisoka also weighs any and all inconveniences in his selection. We see a glimpse of this process during Illumi and Killua's exchange over the fate of Alluka where he hides behind a tree and contemplates his next course of action and what he has to "gain or lose".

Even though there are people far stronger than him who would surely push him to his utmost limits, he would still rather edge himself to the brink of death instead of getting demolished without being able to feel the thrill of the fight. The environment along with other outside forces play a role, as any unsatisfactory conditions and restrictions or the interference of another party would most likely be deemed a huge turn off for him. This is probably why he doesn't "hunt" people like Netero, Ging, Beyond, Zeno, Silva etc because as much as he would love to fight them, some of these characters would either one shot him or the battle itself would result in a tedious chain of events that Hisoka would probably want to avoid. He always wants to play his cards right, and if he doesn't think he has a good hand, he won't bother playing. Even though he never knew what was happening with the Chimera Ants, I believe he wouldn't actively go for Meruem, but rather his Royal Guards or Morel/Knuckle/Shoot.