Once your graveyard is full of badass creatures, reanimator spells like Reanimate and Animate Dead allow you to spend 1-2 mana instead of 6 or more to put your powerful creatures into play, thus allowing you to repeatedly impact the board in ways that only get more unfair as more powerful creatures are printed in new Magic: the Gathering sets
It can really speed up the process of creating a critical mass of slivers, while also giving your deck a lot more longevity and staying power
An eldrazi with a Mindslaver effect is also a pretty great flavor win in my book
If you want to speculate or need a copy for a deck, theres just no reason to wait any longer
After all, it costs Wizards of the Coast no more money to print a common than a mythic rare, even if they have a different value to all of us
Between hasty creatures, quick card filtering, and direct damage, red wants to execute its game plan as quickly as possible