I still dont get why...

Riot removed green wards to punish people for not buying them. Just because people don't buy them does not mean the item is useless or flawed all the time it just separates low elo form high on average I would buy like 7-17 green wards in a game just to keep jglers away from camping my lane or just give vision to my allies to prevent them from making decisions that would otherwise throw the game. And TBH I loved the old upgraded trinket it was the best thing in the game I would always upgrade my red or yellow one it allowed me to give vision without sinking 800 gold and a item slot this change is so drastic it really prevents me from getting a lead in my lane unless I have coordination with my jungler to ward the river with two pinks which 90% of the time they do not. Also the old system was useful for teams that were behnd if the other team didnt have vision it was very easy to make a comeback.

TL; DR basically do not punish the small minority of people who do get vision just because the others don't the old system is what separated low elo from high.