It's a similar value proposition as VSCode/Sublime Text vs IntelliJ. If you are in a database all day and need a big beefy IDE, Beekeeper Studio isn't for you.
I built Beekeeper Studio because I wanted an easy to use and intuitive GUI. I'm not a DBA, so using DBeaver or DataGrip required me to basically re-learn the whole app every time I used it, which I didn't have the patience for.
Hope that helps add some context :-)
Beekeeper seems like a less clunky, but also much less featureful alternative. I mean that in a good way really, I quite like the idea of 'slightly more than psql' (but not too much), as long as it's fast/lightweight.
Currently using TablePlus and while I have a few problems with it, it's snappy and mostly fine. Tried Beekeeper some years ago but might as well try again.