I've done professional GUI programming and there are really only three options that make sense:

1. Write the GUI natively per platform. This is best from a UX perspective but is expensive and you probably need different developers working on different platforms. Other downside is that really advanced functionality is harder to implement and sometimes the performance of native APIs is poor and hard to improve (Apple has this problem frequently).

2. Use a cross-platform framework like Qt (Electron would also go here). This is the most cost-effective solution, but generally does not feel like a native app, which may or may not be a problem.

3. Use a custom GUI framework.[0] Probably the most expensive option and hard to hire developers for, but can be warranted for complex applications like CAD tools, games, etc.

The problem with Rust GUI libraries is that they can't really target 1 or 3 so they need to target option 2. But the big players there are Qt and Electron. Qt is popular because it works well, is proven, and has a lot of financial backing. If you don't need something super complicated a decent Qt developer can get it working quickly. Electron is popular because there are tons of web developers and they can be productive quickly.

Rust attracts a lot of hobbyists who are talented and have good ideas, but I don't think they have the staying power (or financial ability) to provide something that competes with Qt and Electron. I'm sure it can be done in theory but I don't see it happening in practice anytime soon.

[0]: By custom I mean tailored for the type of application you are making, e.g. what a lot of game devs do for their internal tools.