How is that different from other languages that have proper repls? Lisps don't really give you much here, if the language can parse itself and can eval it, you have the sufficient primitives.

What helps is how "small" the hot reloaded parts can get - lisps are good here due to a lot of functions and not much shared state. But that is again, not something specific to lisps, neither are they the best at it - there are far purer FP languages for example