Why?
No, seriously, what's wrong with Tarmogoyf entering Standard? And before you say "it's too powerful!" I'd like to point out as far as I can tell it didn't break the format back when it was originally printed (remember, it was Standard legal in the Time Spiral block!), and creatures are generally more powerful now meaning it'd stand out even less.
It's kind of like how at one point Force of Nature was probably considered really good, but nowadays is mediocre compared with cards like Terra Stomper. Or how Mind Twist was once considered so broken it was actually banned in Vintage, but now is unrestricted and barely sees any play.Uh...huh? Trying to replace them with "less insane" versions (and I wouldn't call them insane anyway, they're not that good) won't change a thing, people will keep playing with the originals. You'd have to print something better to discourage people from playing with them.