It's easier to correct for missing libraries than missing language features, and Python fails horribly at functional programming, apparently by design. That is all.
That said, which extension language ends up being used is very much up to Toady; I don't really have any say in it.
It's the fact that inconsistent whitespace can literally kill a program that gets me. The whole tabs vs. spaces takes on a whole new meaning in Python.
Especially, if we are talking about sharing scripts, which we would be. Yeah, I know most compilers handle conversion, but you have to know whether the author uses 1, 2, 3, or 4 spaces per indent and all that jazz. It's almost as if Python was designed to be horrible to share code. Also, the choice of implementing Python over Lua because of the library selection is quite pointless since the script will mainly be dealing with DF objects and not having to connect to a remote server or something odd like that. Sure, I can see some utility in it, but it's not a staple requirement. (Also, I read that LUA is much easier to integrate with C++ than Python...)
That being said, I
have played a bit with Python and merely only read about Lua, so my support for Lua seems a bit odd seeing that I haven't actually used it, but I still think it's a better choice (if there were a vote.)