I used to think the same thing honestly.
Main dining rooms already feel pretty fancy, especially if you’re not used to that kind of setup. So paying extra on top of an already “included” experience feels weird at first.
From what I’ve seen, it’s more about a few things:
Better food quality or more consistent dishes
Less crowded, quieter vibe
More personalized service
Sometimes more unique menus (steakhouses, sushi, etc.)
But yeah, I don’t think it’s always a huge upgrade. More like a “treat yourself one night” kind of thing rather than something you need to do every cruise.
Some people swear by it, others never bother.