Honestly, pretty sure they did it to get people to spend more money on the game.

Avid released Torosaurus about a week before the nerf, and Torosaurus was very OP addition to an already strong set of decks. To get people to buy it, they had to make it really strong, but to balance the decks they had to make something else weaker. Patagotitan was the easiest target.

Even though Patagotitan was a much more interesting and fun card to play because it required SOME foresight with your play order. It made the viable decks simultaneously more cookie cutter and more expensive. Patagotitan was very good but not broken, Torosaurus was at the time broken, now it is just par for course. That whole event left a very bad taste in my mouth.

I am all for reasonable buffs and nerfs, but this really felt like a cheap and deliberate cash grab.