It's garbage.
If garbage = a martial art/exercise that's been practiced for hundreds of years and continues to be practiced to this day; the most widely practiced martial art in the world, then yes, it is garbage.
People find it useful. You obviously don't like to see people getting use out of things.
Tai Chi is full of nonsense people that will tell you that Chi is "real" and that you'll learn superpowers by learning Tai Chi.
It is probably more nonsense to believe there is such a thing as an 'Ultimate' fighter, and that getting shiny belts is more useful for life.
In reality, it's just a slow motion exercise for Chinese senior citizens.
Where has anyone denied that taijiquan is mainly practiced slow?
I'd love to see any old people get use out of MMA-type training. It simply doesn't happen. That type of training is not useful (or even possible) throughout all stages of life. If youngsters engaging in that training injure themselves, senior citizens would injure themselves even moreso. And what is the logic of training in self defense if the art you're training in destroys you more efficiently than an opponent can?