When you can cast that for free, you can use its ETB to bounce it to your hand as many times as you want
It would require a massive and expensive printing effort on their part, not to mention the hiring of hundreds of people to sort through the submissions and mail millions upon millions of cards
Giving somebody a free card attached to a two-mana 1/1 will, at best, let them make a land drop and pass not a high-impact play when youre already behind, and also far from guaranteed
In the example above, Murderous RiderMurderous Rider is a creature thats a Zombie Knight, has lifelink, and when it dies it gets put on the bottom of its owners library
At the end of the day, Regenerate is clunky, confusing, and not exactly beginner friendly