All these people saying it's "cold" and "harsh".
Why would they want to spend large amounts of time recording, editing, etc. with someone small who will not benefit their channel, when instead they could collaborate with someone who could expand their own channel, thus making the several hours, if not days, producing the video worth their while.
If you had something like 2,000 subscribers, you probably aren't going to spend time recording with someone who has 10 subscribers unless it's because you're friends with them or they have AMAZING content (Which is unlikely because they are just starting out).
Big YouTubers (including people such as PewDiePie) do have shutouts for channels SIGNIFICANTLY smaller than there own, and although it is not the same as collaborating with them, it does help (look at jacksepticeye, he was small before PewDiePiew shouted him out).
Please don't take this offensively (The last thing I want to do is make anyone angry), I'm just trying to put myself in their shoes and think logically
