Ergonomics. It's a handheld. If it's not comfortable for long-term play then it really doesn't matter what capabilities it has. The core ergonomics and weight of the G cloud is the best of any handheld.
Battery life: Similar to the above. It's a handheld. Steam decks just don't have the capacity to last very long on the move. The G cloud, which is either doing light emulation or streaming games from someplace else doesn't need to do much. It's essentially a phone with a nice screen.
When I saw the battery life of the Steam Deck it didn't matter that I had two decades of games with Steam. I'm not carrying around something that bulky with a fan on a trip to Europe.The few times I need to go on the move without a good connection I'm happy enough to emulate something or play an Android game on it. I just don't see how people play SDs without having a power cord nearby, resting them on your knees. As an alternate to a gaming computer the Steam Deck is great, as a support device that targets being a handheld I think things like G Cloud and the Odin are a better target.
The downsides are that it's Android based and altogether a different category. For handheld gaming I wanted something portable that I could play casually. The minor, occasional input or stream lag isn't as big a deal in these scenarios. I'm not playing competitive Counter-Strike on this thing.
I also acknowledge that the G Cloud might not last long in production! The Steam Deck is popular, and the G Cloud might not get support 10 years down the road from Logitech. These portable devices all will need upgrades / updates and I figured I could wait till the next cycle regardless.