1) It is difficult to scape when you use simple quote ' . Hence, it is difficult to write your items.
2) There is no color highlighting ;)
3) When you save the method, strings are not compiled. If you use blocks, you can at least avoid compilation errors.
4) Because at the end what you put in those strings is code, hence, closures are a more accurate reification than string.
5) Strings are now well managed by the system when code is inside. For example, searching senders or refactoring tools wont work with code inside strings, but they do work with closures.

Maybe there are more reasons, but I am lazy to think more.

Cheers
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