So instead of having a separate meta-syntax to manipulate Lisp at the level of the AST, you simply write Lisp. Lisp is the language that's it's own AST. Combine this with a complete exposure of the meta-level of the language, and you get a language where many things that would be very expensive or impossible in other languages are relatively inexpensive and possible.

Smalltalk is nearly it's own AST. There are enough tools and exposure of the meta-level to enable things like Lisp macros, but it's still 2-3X harder than in Lisp. Also, Smalltalk Blocks by themselves are fairly powerful. As a result, people don't use Lisp style macros in Smalltalk even though they could if they really wanted to. (Implementing them would just take a few days.) The cost-benefit just doesn't work out.

(Yes, even Smalltalk is a kind of "Blub" compared to Lisp.)