We just updated the rules a few days ago, thanks for noticing! The idea now is that anyone could visit the reactiongifs stream and find a good gif to post as a reaction anywhere on the internet, rather than super specific ones that were prevalent in the past.
I think the two examples you provided fit the bill, so I featured them. Please have patience with our mod team as we all adapt to the new rules.
There used to be a stream rule about naming conventions (e.g. title all gifs along the lines of "When it snows in April"), but I don't see that rule in the stream description anymore. Few gifs in the stream ever seemed to actually follow that rule anyway.
There are a new set of rules in the description, but they seem really general and I don't seem to see how I'm violating them.
So when I submit reaction gifs with straightforward titles like this imgflip.com/gif/4z4spy and this imgflip.com/gif/4z3766 and they are rejected for violating stream rules without explanation, I'm at a loss