I suspect for two reasons - first, that Tcl is always dynamic the same way and in clearly documented places, whereas PHP is a lot less consistent about it; and second, that in Tcl a lot of the core language constructs do so, so it's something you get familiarised with early rather than bitten by later.

Plus, PHP users seem to be most likely to either go "err, so?" or "YOU DON'T UNDERSTAND THE TRUE GLORY OF PHP!!!" in response to being asked about it, whereas Tcl users generally tend to respond "yeah, you need to learn about that and get used to it" - which tends to significantly alter the next comment made.

(not trying to imply that PHP doesn't have users in the third category, just that the first two are the more visible and it alters the discussion's tone)

Probably because Tcl has other redeeming qualities.

Command line programs are now passe in all except a few niches like routers, chip design etc, but IMHO there still isn't a better "/bin/sh++" that you can embed as command line shell interface between your C functions and the user.

Swig + Tcl + C/C++ works like a dream!