Every once in a while, Magic: The Gathering has a color "boo boo." That is, a card doing something that's out of its color pie guidelines.
Something tailor-made for a green card, for example, is on a red card instead some reason. Or something that is all death and whatnot is on a white card rather than, typically, a black one.
But few cards have ever been a break as hard as the Legends card, Acid Rain. This was back in 1994 when Magic was still in identity discovery mode.
Blue doesn't really destroy. It prefers to counter spells, bounce permanents, and other more control-oriented things.
Acid Rain, however, does none of those things.
"Destroy all Forests in play."
One blue card, all forests are gone (despite there not being a single forest in the art, but that's another matter).
It was made as an after-the-fact mirrored pair card with the green card, Tsunami, which destroys all islands, from the "OG" Magic set.
Since a blue card really isn't set up for total destruction (the only other blue land destruction cards we're aware of are Erosion and Mana Vortex, both from The Dark, and the original core set card, Volcanic Eruption), Acid Rain was kind of out of nowhere.
Mark Rosewater himself called it a "Bad Blue Card" and players, at the time, complained about it a lot.
In short, it kind of broke rules, broke tradition, and just didn't make any sense. Luckily, players don't have to worry about a possible reprint any time soon.
When Wizards of the Coast created their "reserved list" of cards that will never see a reprint, Acid Rain was on that list. So, no worries there.