This is the main answer for the change in tactics. For the risk of getting the ball back, many teams now back their goal-line defence and it limits the attacking structures that the opposition can employ from short range. Most teams like several set-up plays to disrupt the defence, before shifting wide, and you run out of space for that once you close to 20m.
Second reason is the winger skillset has trended towards tall and jump ability, for both attack and defence, so there are clear targets out wide. There's no way the older block-sized wingers would be as good competing for those kicks, guys from a decade ago like Tuiaki or Vatuvei.
Third reason is your 3 primary objectives are possession, position and pressure. Short kicks give you the risk/reward of #1 and #3 at the expense of #2. The most effective way to wrestle control of a game is to maintain possession and stop the opposition from building pressure. Repeat sets create the most pressure of any situation, so you want to disrupt this however possible.
Lastly, something people don't think much about, but even if you don't get the ball back, the attack usually burns 1 tackle defending the short kick, and now you've pinned them to the corner. They then need to waste another 1-2 tackles to get the ball back towards the centre or to try and strip the defence of numbers. It's basically like kicking to the corners when you are in possession.