Cool strawman! People don't say "LGBTQ Lives Matter" as a response to "Black Lives Matter." People do say "All Lives Matter" as a direct retort to people who dare to suggest that black lives aren't being treated like they matter very much.

Furthermore, people who say All Lives Matter are often the same people who don't act like they really think all lives do actually matter (in regard to the policies they support, or whether they wear a mask during a pandemic, etc.), so it sure seems an awful lot like they're just trying to take the much-needed attention away from black lives.

All lives can't matter until Black Lives Matter.
https://www.cbsnews.com/news/all-lives-matter-black-lives-matter/