I have wondered this myself and I have come to these conclusions:
1) Types like water and ice are too closely nit in real life to be separated. (Water freezes into ice and ice melts into water. Common knowledge there)
2) Saves time and money to print out the cards.
3) Makes the card came simpler and more competitive for players.
4) They are just being lazy.
I hope I made some sense and hopefully answered this question correctly. If not, I can always edit this.