Firstly, the CinemaScore for this movie was the same as it was for Full Throttle - an uninspiring B+, which is the kind of indication that studio executives do not like to see on their tentpole franchise movies. It might not indicate outright apathy, but it's not where you want to be. You can't even market the film responsively to that, because it's not low enough to make a point of. So why the cool audience response?
To a certain extent, Charlie's Angels was facing a difficult task from the beginning. Fundamentally, there is simply no reason to tell the Charlie's Angels story again. If there hadn't been the McG reboots of the early Noughties, that might have been different, because it COULD have been marketed as a sort of "woke" version of the IP, redressing the balance of sex appeal and making the Anti-Jiggle TV version, but the TV show isn't what's being rebooted here entirely. Not for the audience, at least.
Audience expectations of a reboot are that it reboots what came most recently, and the narrative here is that we were always getting another go at a franchise that was never great in the first place with no discernible logic other than "why not?" It feels like Charlie's Angels was optioned simply because we're now facing a marketplace dominated by IPs owned by Disney and every other studio is looking to fill their slates with competition for Disney. That sort of manifesto is not going to lead to 100% smart decisions.
It's an ironic reflection, but the way nostalgic IPs have been operating at the minute - with the exception of Jumanji: Welcome To The Jungle and Jurassic World, which were both remarkable successes but also somewhat anomalous ones - a new Charlie's Angels movie SHOULD have brought back Drew Barrymore, Lucy Liu and Cameron Diaz. Elizabeth Banks wasn't a problematic hire, by any means, but this should have been a long-awaited third movie trading on whatever goodwill there was for the original 2000 and 2003 movies, seeking to right the ship the same way Halloween and Terminator: Dark Fate aimed to.
The problem, of course, is that THAT too doesn't necessarily work. Dark Fate plummetted despite being a vastly better movie than Genisys while also seeking to do precisely the same thing as Halloween. Movie making is not a precise art. If there were a specific formula, every movie would stick to it and nothing would fail. But what is very, very clear is that the answer to the Charlie's Angel question that nobody asked was not to reboot.
And then you have to factor in how the production story factored into audience excitement.