Mozilla is struggling. Firefox's market share is less than 3%, in the "also ran" category. Employing all the people in the Silicon Valley to maintain Rust is hugely expensive without an obvious return on financial investment.
By opening Rust up to the community, they ensured its popularity and longevity beyond what more corporate-focused languages (Go, Swift, or C#) can achieve. Relinquishing control is exactly what Rust needed to help its popularity.
Certainly not having a bunch of engineers employed specifically to develop and maintain Rust hurts, but Mozilla simply cannot afford it.
Successful programming languages tend to be bad for business: they generate support costs but little or no measurable income.
The only way to make them profitable is to use them as a lock-in tool for your platform (VB, .Net, SQL dialects...), but Mozilla never had anything to lock people in.
Maybe? But that's not why they did it. In the same year that their CEO took another massive payout they laid off tons of staff "because covid", an excuse that was obviously nonsense at the time but especially looks like nonsense when you realize that tech absolutely exploded during covid with record high valuations.
Mozilla absolutely could have afforded it. Easily.
Mozilla's CEO is an absolutely disaster and the company is never going to be able to recover from it.
How does being the guardian behind the language help Mozilla in any way?
Google has all the resources and hundreds of engineers to throw at Rust. They will definitely have undue influence on the language and its community now that it's in Chrome. I just hope it doesn't wind up looking like Kotlin.
Mozilla has also never really controlled Rust's development, it was their policy to treat it independently. The big tech companies also don't control it now. This might change in the future due to a weakened core team creating a vacuum that might be filled by the foundation, but the current status is that Rust is quite independent.
Everything Mozilla touches dies an undeserving death, so I hope they continue to spiral further down into irrelevance and an eventual dissolution.