We've been asking for a sandbox mode for almost as long as the game has been out. CG won't do it because they can't figure out how to monetize it. They use other lame excuses why, like we won't use it, we'll get bored of it, it'll be a waste, etc. We would use it as long as TW and GAC are around, even if they haven't been updated in 3&4 years, players would use it to practice vs teams and all the new garbage datacrons they spew out of their assembly line, and new characters from their money grubbing assembly line eras.
There are lots of quality of life things players have asked for they ignore because they can't monetize them. They want to spend as little as possible on QA, QOL, "fun" and what players ask for. (Which is why we've got a pirate era when we should have a fix the game era.)