Has anyone got a good explanation why some sites have daily or weekly upload limits instead of monthly limits?

For example my weekly upload limit at iStock is 38/week. If I do a long and successful photoshoot and get around 50 good images, why can't I upload the right away?
Why can't there be a monthly limit like 160/month? I would even settle with less, let's say 130 per month.

Weekly limits sucks, and daily limits suck even more. I really hate sorting my images in different folders to be submitted to different agencies instead of just uploading a bunch of stuff now and then.

must be because of reviewers, so they won�t freak out, it would go from a queue with 40k (usual) to perhaps 10x that..

there is also the fact that we kind of select them better instead of just dumping them but I also believe we all know what to pick to IS..

But that doesn't work with me... my monthly upload limit at IS is about 160 (38/week). I rarely submit more than 60 images per month. Yet it's very frustrating thing to do because of the weekly limit.

Hmm... a new idea... How about if non-uploaded images would add upp to some kind of a "bonus"? Like if you upload nothing or very little on some week, you could upload a bit more than usual the next week?

don�t know if they will do something like that guess not lol but this topic reminded some guys that uploaded over 500 files in a month and I am talking about indies, I wonder if IS have done anything, they haven�t..

Hmm... a new idea... How about if non-uploaded images would add upp to some kind of a "bonus"? Like if you upload nothing or very little on some week, you could upload a bit more than usual the next week?

Or you can upload and finish them all but the surplus sit waiting to pop into que next week.