i'm more thinking about libraries like tensorflow, ssh, or libgit2.

Yes you could rewrite them in Rust, but considering these are tools which are used all over the ecosystem and have massive momentum behind them, your time would be better spent building cool things on top of existing work than reinventing the wheel and trying to convert the ecosystem to something which will (initially, at least) be an inferior product.

The original statement was deliberately opinionated and extreme, but I still feel like the pragmatic approach of reusing existing libraries instead of rewriting them is the best one for the short/medium term (jury's still out on the long term costs/effects).