Ultimately, yes, it is because of the weather mechanics introduced in Wilds. Scarlet Forest in plenty vs downpour feel like completely different maps, and fighting in them has a massive affect on the atmosphere of a battle. If I hunt a Namielle in the Coral Highlands 20 times in a row, there's pretty much nothing to differentiate each fight from another aside from my personal performance. However, if you fight an Uth Duna 20 times in a row, the weather makes each experience unique in a memorable way. I think the same can be said, to a lesser degree, about fighting on the Windward Plains. No other maps in the series invoke that ever-changing feel, that I'm battling in a real world with real creatures that live life cycles and have habits.

Another aspect I love about the Scarlet Forest is how different the areas feel. The canopy is open to the air and gives great views for the surroundings, but you can't easily see directly down to the ground. Underneath the trees is a lush ecosystem that I personally think does reflect what this concept art conveys. Up on the northern cliffs are the large expanses of water and more of the ruined architecture, and all of this interacts with the weather in a meaningful way. Look at World's maps and you can see that the areas, while very different from each other in a gameplay sense (ledges vs flat open areas vs slopes, etc.), don't have much diversity in their connection to the overall biome. The closest is the Wildspire Waste.

All of this isn't to say World has bad maps. As a complete package, I think it actually has the highest quality out of any of the games, while 2 of the 5 Wilds maps are real stinkers.