Lately, it feels like WotC has forgotten some of the players who loved Magic for what it used to be: a beautiful game set in a beautiful fantasy world.
Universes Beyond sets have started to dominate, and while some “in-universe” sets are still fantastic, the pace of releases has become overwhelming for many.
So why create a new format? What's wrong with the existing ones?
For starters, they all allow UB. Other IPs can be fun and bring in new players, but not everyone wants SpongeBob swinging at your Serra Angel while Sonic blocks Sephiroth.
Older formats are also expensive and tough for new players to enter (think dual lands for Legacy, Power Nine for Vintage).
To be clear: that's okay if you love UB or any other already existing format, play what makes you happy. Uncle Istvan is just a home for those who prefer Magic without it.
Moral of the story: If you want a format that feels like Magic before UB crept in, stays affordable, fresh, and doesn't burn you out... welcome to Uncle Istvan!