Comment by Blikkentrekker

Copyleft doesn't work well with Rust's ecosystem of many small crates and heavy reliance on libraries alongside static linking.

If one library be GPLv2 and the other GPLv3 they couldn't be used together in one project. LGPL solves nothing because it's all statically linked anyway. And yes, one could licence under both under the user's choice but then GPLv4 comes out and the process repeats itself, and yes one could use GPLv2+ but people aren't exactly willing to licence under a licence that doesn't yet exist and put blind faith into whoever writes it.

Using anything but a permissive licence is a good way to ensure no one will lose your library and someone will just re-implement it under a permissive licence.

C is a completely different landscape. Libraries are larger and the wheel is re-invented more often and most of all dynamic linking is used a lot so the LGPL solves a lot.