They because they haven’t used it yet, or played any games worth talking about (queue dummy asking for a list of good games even though lists have been provided a billion times on here).
Now as far as why it has struggled/failed in a sales figure sense; it’s because the cost of entry is higher than the experimental money the general public is willing to spend. It’s way easier to roll the dice with $60 on a game you may not like but you’re familiar with the experience. Dropping $300+ dollars on a peripheral is a steep gamble. It’s absolutely worth it, but I don’t fault people for being apprehensive about it.