Georgetown alum here and I can definitely vouch for this. While most students across the country would have to take an entire summer for an unpaid internship on The Hill while living in a very expensive city, our students can do this as an extra curricular during the academic year while living out of their dorm.

Plus if you're already doing political stuff in the city as a professional, the law school is not only the best in the area but one of the best in the country, which makes it a common choice for those in that line of work.

And let's not forget that this is just people affiliated with the university, which could include members of congress who teach classes at the school, not sure what the congressional roster is like right now but for example Madeline Albright teaches a very popular foreign service course.