(Talking about CL) Isn't gradual typing with a typed standard library enough? Because that's kind of what SBCL provides.

Anyway, some other reasons:

* Baby ducks who can't get over the parentheses (which quickly become invisible to the eye, you read Lisp via its indentation).

* Baby ducks who can't get over too weird/big differences from C/C++/C#/Java/etc... like CL's compilation model.

* ML typing being /the/ fad these days.

* Low-level fetishism. I know a lot about this, since I've had my own C weenie phase (you know, the kind to spit on GC by principle) as a young university student, before turning smug lisp weenie ten years later; Tcl was actually my gateway drug into useful homoiconicity.

* Some hard technical limitations:

  * No user accessible parametric deftype.

  * No recursive deftype (so no typed lists/trees).

  * Gimped hash tables (untyped, lacking literals thus read/write transparency).

  * CLOS being bolted on instead of truly integrated in the language; would need a JIT and something like https://github.com/marcoheisig/fast-generic-functions on system classes to go fast enough, Julia kinda does this (but it hurts my eyes).

  * Lack of LSP; no, SLIME/Sly isn't the same, as you're lacking lexical information that allows to complete/rename stuff.

  * And hundreds of other rust spots sometimes fixed by extensions (e.g. gray streams, extensible sequences) or libraries (loop -> iterate, trivia), very often crutches in look and feel.