That's because this combination gives you access to four colors and two commanders with generically powerful abilities
It can always sacrifice itself as a one-shot proliferate effect too
Number 152 Language English Legal Formats Alchemy, Brawl, Commander, Competitive Brawl, Historic, Legacy, Modern, Pioneer, Standard, Timeless, Vintage Rulings (4/15/2013) Returning Maze's End to its owner's hand is part of the cost to activate its last ability
Brenard also works as typal support for Golems, which makes it the perfect commander for a "Splicer" deck, since all of the Splicers fall into these colors
Compare its 5-mana minimum investment to something like Contagion Clasp or Contagion Engine
It was fine in RDW when you didn't have a Hellrider and so on and so forth