Straight home-and-away aggregate completely neutered home-field advantage.
New format this year. I wasn't aware either until a month or two ago.
My guess as to why is that it guarantees every club that makes the playoffs has one meaningful home game that fans can attend. That was the case before with the aggregate two-legged format yet they went away with that by switching to single-elimination.
Works great for things like the Champions League, where the teams aren't really seeded, but it's not ideal for playoffs.
This best-of-3 format isn't my favorite, especially with a penalty win counting the same as a 7-0 in regulation, but I get the thinking behind it.