This is a tricky one, honestly, because the steam deck straddles the line between PC and console.
If you were a Sony fan, you'd be rightfully upset if Sony released a new PlayStstion every year, and made new games only for the new hardware. It's just not long enough to feel the hardware has ran its lifespan, and you feel cheated.
Conversely in PCs, the expectation is that the hardware slowly improves constantly, and new hardware doesn't stop you playing all the latest games on your old hardware; the only limiting factor is how far your old hardware can be pushed before the performance is too poor. And that is YOUR choice as a user, not an artificial choice imposed on you.
I'd expect that any Steam Deck 2 is going to be more like the PC model - it won't create exclusives or stop people playing the new games on their old deck, it will simply be better and faster.
So on that basis I wouldn't personally have a problem if Valve put out a deck every year.
All that said however, I think waiting several years is the smart business move. People have longer to enjoy their hardware while still feeling like they have the "latest model" - it's psychologically better from the consumer perspective.
There may also be an argument that longer release cycles makes things less complicated for devs (less devices to test on) and also keeps the hardware going for longer, because devs will be incentivised to optimise performance for the current deck (which they might not be as much after a new one comes along)