1. Politics - whether it be the NBA putting Black Lives Matter on the court in the Orlando bubble or Mavericks owner Mark Cuban announcing he'd no longer play the National Anthem before Dallas homes games. The "in your face" manner that the NBA handles politics is very off-putting (to say it mildly) for a large segment of the the US (many of whom used to be fans but no longer).
2. Player movement - LeBron James, Kevin Durant, James Harden, Kyrie Irving and others have all now played for multiple teams and treating fan loyalty like something that is disposable is harming fans willingness to consume the NBA's product. Plus the way that many of these relocations happen is also distasteful to many fans (looking at you James Harden).
3. Too much ISO and 3's - there's way too much isolation play and too many three point attempts. Watching someone try one-on-one moves or kick out for a 3-point shot is boring basketball. Sure simple math says 3-points are better than 2-points but for the viewer 3-passes before a shot makes for more exciting play. In a way the point above was about too much player movement (from city to city) and this one is about too little player movement (on the court).
4. China - this is separate from politics because even many who support BLM are upset with the NBA's kowtowing to China. It was naked crass greed and very repellant. LeBron James wants to lecture me on human rights but defends China? Go fuck yourself.
5 Costs - there are no fans at games right now but even when there were the cost to attend games was getting out of reach for the average fan. It is not a stretch to say to be a season ticket holder these days you'd have to be earning at least six-figures a year. Taking away access to attending games in person hurts a person's desire to watch that same product on TV. Covid precludes people from attending today but the very costs (tickets, parking, concessions, etc.) having been putting the experience of attending a game out of reach for years.
I could also include the awful way replay is being handled, especially in the last minutes of the games and the refereeing of games in general but that's a post for another day.