Not true for most of the big hitter crates. MSRV is a big thing and I never understood why, but it was recently explained to me it was so the old tool chains in distros could keep compiling, so the big crates tend to bump MSRV very slowly. Obviously, each project owner decides this on their own, so it isn't universally true, but is common practice.
Theres also talk of improving the situation, including
- Depencency MSRV errors explaining how to downgrade (merged)
- The dependency resolver skipping versions that need newer Rust. To have reasonable errors, this will require the new pubgrub resolver. The main question is opt-in vs opt-out
- Warnings when using functions newer than your MSRV
