There's that, and it's a significant factor too, but something else changed too and it's arguably even more significant. Mainly, that Phantasy Star Online and Phantasy Star Universe game out in an era where the gameplay was a lot more slower paced and dungeon runs took longer. In contrast, Phantasy Star Online 2's gameplay is more bite-sized and quick paced.
The original Phantasy Star Online on Dreamcast had only four real zones to explore: the Forest, the Caves, the Mines, and the Ruins. Each of these areas was significantly longer and lengthier than anything you'd find in Phantasy Star Online 2. Likewise, when PSO Episode 2 came out on the Gamecube, we had the VR Temple, the VR Spaceship, the Central Control Area, and the Seabed added. All four of these are fairly massive and lengthy to explore. Any one of them will take about 30 minutes to an hour for an appropriately equipped character at the appropriate level for the difficulty. They can take longer too if you're unprepared or doing them for the first time on a particular difficulty level.
In contrast, Phantasy Star Online 2 (OG, not NGS) areas are far more bite sized. You run through the Forest exploration very quickly, and it's only due to randomized events that you might be there more than 30 minutes. The same is true of every other exploration event. Most of them don't last very long. Likewise, the Emergency Quests that appear in game largely lasts 30 minutes at best, and most can be completed sooner than that. It's a much more speedier game in terms of how questing and dungeoning and such is completed. That gives it a VERY DIFFERENT FEEL from the original Phantasy Star Online, and to a degree, Phantasy Star Universe as well. Everything is just so fast paced in comparison. You blitz through packs of enemies. Regular enemies are rarely a threat to you. You're primarily looking for randomized events and bosses now.
It makes sense - Phantasy Star Online 2 was clearly designed around the emerging gameplay trends of modern gamers, especially Japanese gamers. It's very similar to how most dungeon runs in Final Fantasy XIV aren't designed to take exceptionally long as well. But they lost some of that magic that made the original feel so great in the process. So that's why we keep having a "I want a remake/port of PSO1" thread every so often despite PSO2 getting a western release.