"WHY have the maps been updated like this???"
Each sheet had variants for every state that the map was in; All levels uncleared, all levels cleared by Mario, and all levels cleared by Luigi. These all had to be multiplied by 4 to account for all the animation frames, then doubled to account for the palette change when opening your menu, and then multiplied yet again by the amount of screens there were (ie. how many positions the player could scroll the screen to). And let's not forget the fully stitched together map which also had 3 variants multiplied by 2 to account for the palette change.

Needless to say, this ballooned each sheet to gargantuan size, the biggest of which being World 6 at a size of ~5000x2000 pixels. While TSR is no stranger to large sheets (any character from the Mario & Luigi games, for example), having such large sheets for an NES game, especially when most of it is redundant information anyways, is absurd. I mean, they were so big that large enemy sprites were inserted into the massive empty space left over.

"Why on earth do I have to go and replace every single bit of an edge on maps?! This just added more work!"
While I can sympathize, it's a small price to pay for a more convenient size and better legibility. Besides, they're very small images that have clear legends that show you where each piece goes, so it really shouldn't take that long to figure out where everything goes.

That said, a good compromise would be to add animated gifs for each assembled screen. That way, people can take those frames more readily without making the main sheet super large. I'd do it myself, but I'm not too familiar with the correct timing of it all. Best to leave it to someone more familiar with the game's animations.

WHY have the maps been updated like this??? I looked through all the other ones and this is INFURIATING. Why on earth do I have to go and replace every single bit of an edge on maps?! This just added more work!

Well it is SMB -3-

Why is there an "III" in the 3rd screen???

Yes, in the SNES/GBA versions, the Worlds are named Grass Land (unchanged), Desert Hill, Sea Side, Big Island, The Sky, Iced Land (mostly unchanged), Pipe Maze, and Bowser's Castle (even though most of the world takes place outside said castle). The Japanese and original American release also had these same names (well, for the most part; Sea Side was originally Ocean Side and Bowser's Castle was originally Castle of Koopa), but the American "Rev 1" re-release and the European version changed them into the more boring "Something Land" names.

Wait, Desert Hill is an alternate name for Desert Land? That must be how the course in Mario Kart DS gets its name!