At least in the government sector, time-limited post-employment restrictions are not uncommon. They are intended to avoid the appearance of impropriety as much as actual impropriety itself. In those cases, we don’t trust the departing employee not to use their prior public service for private gain in certain ways.
This is also a massive burning of the commons. It is valuable for forecasting/evals orgs to be able to hire people with a diversity of viewpoints in order to counter bias. It is valuable for folks to be able to share information freely with folks at such forecasting orgs without having to worry about them going off and doing something like this.
However, this only works if those less worried about AI risks who join such a collaboration don’t use the knowledge they gain to cash in on the AI boom in an acceleratory way. Doing so undermines the very point of such a project, namely, to try to make AI go well. Doing so is incredibly damaging to trust within the community.
My argument for this being bad is quite similar to what you’ve written.