Cards like Thundermaw Hellkite are fantastic threats too, and great finishers, but they rarely do the whole job, they rely on other cards having done a lot of prior work
But building a Commander deck has also become an increasingly complex process
You then get to cast that spell for free
Sure, itll save your creature from several removal spells, keep it alive in combat, or ambush fliers, but it wont help it trade up in combat or get in the last several surprise points of damage
Enchanted cards usually have alternate art and special foiling that make them look amazing
Its card draw rather than milling or discard, but that just makes it that much more of a fit for a wheels theme