Why prefer scripting instead Qt/C++ on webdevelopment?

[wysota]

Yeah, for instance python is sweet as well in expressing code and ... .
But is writing less code can be best reason?

Yes.

if you mean less code i prefer using ruby for it but you know ruby gonna be worse after a while on performance.

Ruby is also a scripting language. And since the script only runs for a couple of seconds, such drawbacks as you describe are not significant.