A 500MB Electron app can be easily a 20MB Tauri app.
In either case you end up with a fresh instance of the browser (unless things have changed in Tauri since last time I looked), distinct from the one serving you generally as an actual browser, so both do have the same memory footprint in that respect. So you are right, that is an issue for both options, but IME people away from development seem more troubled by the package size than interactive RAM use. Tauri apps are likely to start faster from cold as it is loading a complete new browser for which every last byte used needs to be rad from disk, I think the average non-dev user will be more concerned about that than memory use.
There have been a couple of projects trying to be Electron, complete with NodeJS, but using the user's currently installed & default browser like Tauri, and some other that replace the back-end with something lighter-weight, even more like Tauri, but most of them are currently unmaintained, still officially alpha, or otherwise incomplete/unstable/both. Electron has the properties of being here, being stable/maintained, and being good enough until it isn't (and once it isn't, those moving off it tend to go for something else completely rather than another system very like it) - it is difficult for a newer similar projects to compete with the momentum it has when the “escape route” from it is generally to something more completely different.
Turns out modern ubuntu will only install Firefox as a snap. And snap will then automatically grow to fill your entire hard drive for no good reason.
I'm not quite sure how people decided this was an approach to package management that made sense.