I think (it seems) the longer ones you post show as a video, while the short ones just show as a clickable link.
people are more likely to click a video clip they can see is an actual video more often than they will click a clickable link that they are unable to see until after it's open.
(
![Unsure :unsure: :unsure:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
does that make sense?)