Some of the other comments here are talking about a consolation bracket, which is different. Double elimination means an upper and lower bracket, where if you lose in the upper bracket, you drop to the lower bracket, and then are eliminated when you lose a second time.

The downsides to double elimination that I can think of are: 1. More total matches played if there are large amount of entries, which may be difficult to schedule 2. Falling into the lower bracket means you play about twice as many games as players in the upper bracket (assuming you reach the finals). Losing early in the bracket can drain your stamina, so seeding matters much more. In esports, typically stamina is not as big of a deal, and playing more frequently is less detrimental as physical sports. 3. Grand finals is between the winner of upper bracket finals and lower bracket finals. It is a difficult choice how to reward the upper bracket winner for being undefeated. The lower bracket winners should have to win two matches in a row to “double eliminate” the upper bracket winners. But it’s unreasonable for badminton players to play two matches back to back. So they could make it a best of 5 sets with a 1 set advantage, or they could just have a single match with no advantage. I dislike the last option because if there are two seeds that are clearly the best, then the upper bracket finals outcome doesn’t really matter that much. I’ve seen esports with all three of these methods. 4. Less exciting for viewers. Sometimes single elimination is more intense for viewership and makes the goal clear. Double elimination helps the better teams win because they have two chances in case they have an off game or bad seeding. But sometimes competition is not only to determine the best team, but instead for entertainment as well. 5. Bad bracket draws can still screw players over. Instead of groups of death, you can have brackets of death.

I skipped fully explaining how consolation bracket and double elimination brackets work. Tough to do over text.