Preprofessional vs. professional

Why would a student pursue a pre-professional program in architecture vs. a professional program? Is it for someone who's not sure if they want to pursue architecture? What kind of job would they get upon graduating? I realize they would need a Master's program after that to pursue a career in architecture.
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First, let me put your question in another context.  Instead of asking preprofessional vs professional, a better question is professional vs. professional.

NAAB (accrediting board) accredits three degrees - 1) Bachelor of Architecture (5 years); 2) Master of Architecture (4+2/3 years); and the Doctor of Architecture (only at Hawaii).  So, students can choose from any of these three paths to a professional accredited degree.

Thus, students pursue the 4+2 preprofessional degree + the Master of Architecture because it provides a broader undergraduate education; it provides the opportunity to pursue studies at two institutions/programs - one for undergraduate and one for graduate -- as well, it allows the opportunity to take time off between the two degrees.  Finally, many of these 4+2 programs do not require studio in the first year allowing a student to ease into architecture compared to the five-year BArch.

Students with the four-year preprofessional Bachelor of Science in Architectural Studies can secure any entry level position with an architecture firm; just because they do not have the professional degree, does not mean that they cannot contribute their skills to a firm or any employer.

Ironically, in the early 1980s, there were about 90 BArch degree and 50 MArch; not it is opposite with about 90 MArch degrees being offered and 50 BArchs.

I hope this helps.  Thanks!