As a person currently interviewing with companies (student, graduating, etc.), I definitely wouldn't be able to commit to a week long trial process, even if paid, in the next 6-8 months. (Unless over Christmas/New Years; even the week long Spring break is nearly 6 months out.) I'm hoping (fingers crossed, etc.) that I'll have a job lined up in the next two months; I don't want to be looking for a job in 6-8.

Asking someone to drop everything for a week (particularly with what is likely a month of notice, if that, given how long hiring processes seem to take) seems ridiculously presumptuous about what people's motivations/etc. are. I'd imagine that many good candidates also just have other things in their life: such as responsibilities related to children. I know that I have a hard time re-arranging my responsibilities (to my grad classes, both part time jobs with very flexible hours, and to a lesser degree to extracurricular organizations) so that I'm free to spend a day or so travelling for a day long interview with a month's notice: and I'm a student with (supposedly) all the free time in the world and a much more flexible schedule. I don't see where working professionals with (supposedly) more rigid schedules and more obligations (work, sure, but also family or any other obligations in their lives) would find the time to spend a full week interviewing (assuming the weekend is spent travelling, so that the full work week is available).