Why shouldn't it be Electron? Should it be GTK? Why not QT?
Linux doesn't have a standard desktop environment or widget toolkit. Electron doesn't seem like a worse choice than the other options, and it's easy to find engineers who know how to work with it.
1Password doesn't just store passwords. It has a bunch of other features. It's a fairly complex app at this point. It also has fairly similar user experiences in Windows, macOS, Linux, iOS, and Android, and that's pretty hard to pull off. If Electron helps them accomplish that, that's fine.
Because Electron bundles (light) chrome and nodejs and all deps breaking desktop integration and security (the developers are now responsible for checking vulnerabilities in all bundled libraries and they are not doing it).
Those are pretty good reasons not to use electron.
Because every Electron app is inconsistent with the rest of the desktop. I use a dark theme system-wide but Electron won't care [edit: 1Password has custom integration for GTK theme]. Honestly, this isn't something the developer of the app have to put years of research in (Slack for example). The toolkit is supposed to do the integration (GTK, Qt, [Cocoa?]) and clearly Electron doesn't care.
> Why not QT?
You tell me (assuming you're talking about Qt, not QuickTime)
> Electron doesn't seem like a worse choice than the other options
Not really. Its just that its lazier/cheaper to just get your web development team pretend to write a desktop app. I get it, business decisions need to factor cost into account and hence the choice. I understand when a business says "we just don't have the funds to use a proper app framework, please do with what we have for now". But instead everyone goes to pretend like Electron apps are perfect even though the reason it was chosen was almost completely based on cost.
There are also advantages for the user. For example, new features arrive for all platforms at the same time; there is no prioritization of platforms or such. Same for bugs - apart from issues stemming from Electron itself, they're likely to appear on all platforms and therefore likelier to get fixed.
In essence, the old "only X% of our users use platform Y, it's not worth it to make this feature/fix this bug for them" does not exist anymore with something like Electron, and while this is ultimately also a cost consideration, it does come with benefits for me as a user, especially if I'm on a minority platform.
None of this is even relevant in this case, since they use (I hope) Cocoa/UIKit/whatever it's called on macOS, so there's anyways not _one_ framework used everywhere.
Linux doesn't have a standard desktop environment or widget toolkit. Electron doesn't seem like a worse choice than the other options, and it's easy to find engineers who know how to work with it.
1Password doesn't just store passwords. It has a bunch of other features. It's a fairly complex app at this point. It also has fairly similar user experiences in Windows, macOS, Linux, iOS, and Android, and that's pretty hard to pull off. If Electron helps them accomplish that, that's fine.