People with deep pockets are typically advised not to depend on unsupported infrastructure. It is hard and, often, unwise to argue with such advice.
It is still early days. Give it ten years: Rust will either have taken off or sunk, by then. Maybe somewhere in those years there will be some new hotness to jump on instead.
Either way it's a short time in which to gain acceptance anywhere near the level of C++ so it's not surprising it hasn't. Although companies (including Microsoft and some Google teams) are just starting to take it seriously.