Just to get everyone caught up: an individual Pokémon has several traits that can affect its battle performance, with some of those traits being unchangeable, and some being changeable but with varying degrees of difficulty. In a competitive environment, generally the most important things are the Pokémon's Individual Values (IVs)s, Effort Values (EVs), Ability (often Hidden Ability), Nature, and Moves (often Egg Moves or Event-exclusive Moves).
In the case of Pokémon with event-exclusive moves or abilities, you'd need to find someone willing to trade one to you, or be lucky enough to have your own from the event. If the Event Pokémon in question is from a very old event, this causes another issue of long-time players having a grandfathering advantage.
From this, we can see a motive for creating idealized Pokémon through hacks - these players know how to battle, they know what strategies are effective and counter each other, they know how to read their opponents and respond accordingly. But they simply don't have the hundreds of hours needed to sink into making a team. Perhaps we should sympathize with the cheating, then?
There's another side to this however. Pokémon’s game releases over time have steadily added ways to change a Pokémon’s traits more easily, and generations VIII and IX have made almost all of the unchangeable traits changeable without having to hatch or catch a fresh new Pokémon. IVs? Use Bottle Caps and your IVs are maxed. Ability? Change it with an Ability Capsule for a standard ability, or an Ability Patch for a hidden ability. Nature? Change it with a Mint. Egg Moves? Teach 'em with a Mirror Herb in a picnic, no breeding needed. Event-locked moves? They're out - Sword & Shield require that you wipe 'em for the Pokémon to participate in competitions, while HOME automatically wipes 'em if you transfer to any other game from Generation VIII onwards.
Now, you do still need to grind things like Pokémon Dollars and Tera Raid Battles to get the materials for some of these changes - but that ends up taking much less time than biking in circles to hatch hundreds or thousands of eggs. So then, is cheating really justified to "skip the grind" when doing it legit is now easier and faster than it ever has been?
Pokémon clearly doesn't want people to cheat, and they've extended an olive branch by making it significantly easier to do things legit. Why not return the favor and play by the rules? It can't be as hard as it used to be.