As scottmcm says, in order to get access to testing hardware, specifications documents, code libraries, and all the other material needed to develop full support for a gaming console, you generally have to sign an NDA and a development licensing agreement that heavily restricts what you're allowed to do with those tools. This is a business decision by the console manufacturers, to ensure their control over what gets released on the consoles, and if you violate that NDA, (a) your games get pulled from various app storefronts, (b) your code signing keys get yanked, and (c) sometimes you get sued, for not-insubstantial amounts of money.
I agree with you that it would be great if Rust, out of the box, supported cross complilation for the PS5 or the Switch. Chucklefish developers have stated that getting Rust working on the big-three consoles (at the time the PS4, Switch, and XBox One) was feasible, but they cannot contribute that work back to the Rust community without violating the NDA they signed to get access to the development materials in the first place, so they're kind of stuck. I've heard since then that the team is no longer using Rust, because of hiring issues rather than technical issues, so that work is likely no longer being maintained internally at Chucklefish, too.
Until such time as Sony, Nintendo, Microsoft, &c see fit to support Rust, sadly Rust will not have first-class support for consoles, no matter how committed the Rust community is to that support: developing and testing compilers targeting those platforms will require a change in how those businesses operate. As consoles use more and more off-the-shelf hardware, porting Rust will get easier and experiences like Chucklefish's may get to being more common, but for now, we're stuck. The most we can do is advocacy, and frankly, none of the big three have shown much interest in opening up their platforms to wider developer audiences. Even Microsoft has slowly moved away from programs like XNA, and that was pretty locked down even in its heyday.