The biggest issues with modern day Pokémon began popping up years before Gen VI, but Gen VI is seen as the starting point specifically because it lacked a lot of meaningful single-player content like many of the games before it. People were initially forgiving because it was a jump to 3D, but ORAS was a massive red flag that things weren't going to go back.
I can forgive HGSS and its new issues because it also brought a ton of new worthwhile content with it. But more recent games make these issues far worse while simultaneously being short on worthwhile content and also raising the asking price. And it just gets worse and worse.
Let me put it this way. You have a route in Gen IV that makes use of grass encounters (Bidoof, Pachirisu, Buizel, West Sea Shellos), water encounters (Wingull/Pelipper, Tentacool/Tentacruel, Shellos/Gastrodon), fishing encounters with the three rods (Magikarp/Gyarados, Finneon/Lumineon, Shellder), honey trees (Aipom, Heracross, Wurmple/Silcoon/Cascoon, Burmy, Combee, Cherubi, Munchlax*), the Poké Radar (Hoppip), dual-slot mode (Elekid with FireRed), a special encounter (Drifloon), and a second half that is counted as the same route but has different encounter tables (Hoothoot, Beautifly/Dustox, Kricketot, Budew, Psyduck/Golduck, Barboach/Whiscash, Slowpoke, Skiploom, Lotad). And consider the evolutions too (Bibarel, Floatzel, Cloyster, Ambipom, Wormadam/Mothim, Vespiquen, Cherrim, Snorlax, Jumpluff, Electabuzz, Drifblim, Noctowl, Kricketune, Roselia, Roserade, Slowbro/Slowking, and Lombre/Ludicolo). And this route doesn't even have swarms.
There are so many reasons to keep coming back at different points because the game keeps giving you new encounter methods as you progress. But then look at something like XY where you can encounter like 20 different Pokémon on a route the first time through without any conditions. It just feels lazier. Or how hundreds of Pokémon were just shoved into the Friend Safari.
