My experience as a scientist (5 papers published) is that often times it is not required by the journal to release the code which was used to create the results. That is not saying that journals would not accept the scripts. Many journals allow online supplementary material. Some journals geared towards algorithms and such (e.g. Computers and Geosciences) require you to add the source of an algorithm, but this is more an exception than a rule.

In addition to the culture at the journals, for scientists code is just a means to an end. Many are not professional software developers. Because many regard the code as just a tool to express science, they do not feel the urgency to also publish the code. In addition, polishing your code to the point where it could be published takes a lot of work. A scientist is paid to do science, not write software.