What I struggle to understand though, is why can't anyone in her life get her the help she clearly needs.
How?
The conservatorship she was under didn't work; and she should never really have been under the care of her father - but generally, people's fathers look out for them. Amanda Bynes was also in a conservatorship under the care of her parents, and look how differently that turned out.
But both are troubled. Bynes has bipolar; and as is typical for the condition, lashes out at the person and people who "control" her. Fortunately for Bynes, she also has periods between relapses where she is stable, and she can apologise, and she has insight into her own decline, where she can get help. I suspect Britney does not get many of those.
My mum had bipolar. She did a lot of what Britney does; albeit thankfully not as publicly, as she died before social media was as big, and she's obviously not famous. She bounced between home and a mental hospital for my childhood; until she died. I often saw her when she was restrained; she wasn't allowed to make any decisions herself. The "highlights" of our time there was when she was allowed into a very secure garden area.
Bipolar is a hell of a beast. Lithium and other drugs can massively help; but bipolar's MO is that you don't believe you have it, or that you need help; and take yourself off the drugs. You strongly believe it's someone else's fault, they've tricked you, they're taking advantage. That must be even harder if it's more severe, AND people are actually taking advantage of you.
Free Britney gave her freedom vs her Dad, but she's lost a lot too. Her marriage - and they genuinely seemed fond of each other. Her relationship with her sons. Allegedly meeting Elton; and her appearance at Glastonbury.
It's so nuanced. It's almost impossible to keep someone safe who doesn't want to engage. In my mum's case, she had many children and was taken to court to try and force sterilisation. It's not clean-cut for anyone. It must be a million times harder with a couple of million experts thinking they know best because they loved her in the 90s.