Even when money allows for this, it's not always possible to segregate the work. I.e. a scientist may fully understand the mathematics of his work, but not understand that translating the math directly into code will cause serious performance issues. A programmer should understand the performance issues, but without a deep and intuitive understanding of the mathematics, including what assumptions are implicit therein, will often have difficulty making the translation.

In many cases, projects with sufficient technical depth require detailed domain knowledge that can be acquired quicker and cheaper by hiring scientists or engineers with that knowledge and then teaching them to code (or code better), rather than segregating the work and dealing with the problems that result from the communication gap.