Most of the businesses where lot of Nepalis work (mostly restaurants) are closed on Tuesdays, therefore, it is logical to have parties on Monday night.

Sure, it does not match the schedule of students and office workers.  But most of them don't show up in Nepali parties anyway.  I have heard from not one, not two, but many so called "white collar" Nepali workers that they proactively avoid Nepali gatherings.  They have their reasons, who am I to judge.

So, yes, it does make sense to have Nepali parties on Monday nights.