Valve make no profit on the consoles themselves right? And if the steam deck profit model of making their money off of games applies to games bought on any handheld, then why not let the other companies have the higher end market and all the research and development costs that making a new console needs. Especially because each new generation would need a refresh to stay on top.(more r and d costs) So why wouldnt valve just keep making their current steam deck that runs stuff well enough for them to keep selling games.
their system is barely out and its a niche product on a growing market of niche portable gaming pcs.
announcing a steamdeck any sooner than they have any need to would only harm their profits with the hardware, which currently are strongly leveraged on them being the price to performance winner.
also a new system would be much more expensive and that will make it much harder to sell their stuff