It is a bit chicken-and-egg; the only way a curious programmer would get to see a full-blown commercial Lisp is if they were already working somewhere that had bought it, and if they were they would probably already be a Lisper.

Admittedly I haven't researched this in depth, but I don't think any of them do a "free for non-commercial use" edition without severe restrictions. Even Oracle, one of the most ruthlessly commercial companies in the software business, lets you download for free to kick the tyres...