Nexon's hubris was adding a **** tonne of new servers during their prime. Obviously now it would be logical to have just 5 or 6 worlds like the old days with just Scania, Bera, Broa, Windia and Khaini. More worlds divide the playerbase, and even if people are given to option to world transfer, they're reluctant to move a single main because link skills and other stuff.
Many outdated parts of the game were changed, which in effect made the game less social. - Duration of travel from Orbis got significantly reduced - Dimension Portal allowed people to travel to almost any map really quickly instead of manually walking - Solo grinding yields better exp than pqs in almost every level bracket except RNJ. Which got nerfed because it was ridiculous, but instead of implementing other incentives for people to PQ, they just nerfed the exp. No more KPQ, LPQ, Carnival PQ etc which were fun.
After 12 years Nexon still bad at handling hackers, drove away a bit of their legit playerbase because of the dumb decisions, and banning both hackers and the people who unknowingly bought duped items. Some stuff are beyond Nexon or the player's control, like the shift in the game market. MOBAs are really popular now, and games like MS, a heavy P2W Asian mmo just won't do as well.
GMs just follow up on reports, that's their job and it is for most games. Nexon's customer support is hilariously bad, and maybe there are incompetent GMs in-game, but that's not even the source of the hacking problem. Removing Star Planet was good, since there's a lot of client-sided hacks.
Making the account creation process longer is a solution that's been suggested for years GMs observing hot maps that are common for hackers like The Dark World Tree and Scrapyard should be given the highest priority Maybe a developer should even buy blight service from XXXXXX website and be more proactive with counter-patching
These things help reduce hackers, not hiring 'competent' GMs kek. Maplestory is not a game where community volunteers should be recruited especially from fan sites and forums, or you're just going to end up with MLC v3.