>>29205516I know what I fucking said.
In Gen I-IV, HMs were the primary method of creating roadblocks. To give one example in the first game, you have thorny bushes (that's what the Cut trees are meant to be, since they're displayed as such in the modern games with 3D graphics) blocking your path to Diglett Cave at the start, forcing you to head to Cerulean. The same type of bush prevents you from going to Lavender until you go to Vermillion, same with the Vermillion Gym. Once you get the HM from the S.S. Anne and beat the second Gym, you can access all these places at once, opening up a relatively large part of the world. Not all HMs are mandatory like this, but the ones that are can be used well when prepared like this.
In Gen V and VI, they have to create artificial roadblocks as the ONLY type of roadblock, NPCs standing in your way and such. It's not that the older games didn't also have these, the original game has a trainer blocking you from progressing until you beat Brock with the reasoning of you not being strong enough to handle Mt. Moon, but Game Freak has to come up with a much larger amount of these, and Game Freak is fucking lazy, so we end up getting fucking lazy roadblocks that make no attempt at feeling natural to the game world, such as Dancing For No Reason and the Kalos Badlands grunt, or the Lumiose Power Outage that easily could have been a believable roadblock if not for the NPCs that were allowed to walk past the guards. The guards didn't block anyone from travelling through Lumiose except you the player, because it's an artificial roadblock with no thought put into it.
It's not just a nostalgia thing, it's about the cohesion of the region. HMs make sense as roadblocks, they are terrain you cannot cross before getting the HM, even if the presentation didn't always make sense due to graphical limitations like
>>29205545 said. When you remove HMs the replacement roadblocks Game Freak creates don't always hold up, which hurts the region.
