Sure, you have to capture the audience somehow, but the thumbnails show the most poignant scene in the episode and sometimes the whole drama. It’s crazily absurd !!
For instance, you’ve just finished episode 12 of everyone’s favourite Cdrama, The Hidden Flower in My Garden 
(made-up title just so you know), where the two 
struck lovers have decided that their relationship is way too burdensome on their disapproving family, so the best decision is to part ways.
The thumbnail for the next episode, however, shows them kissing. What’s up with that ?! They just broke off and now what ?! Kissing ?! I’m sure something happens along the way to change their mind, but I don’t want to be spoilt by some thumbnail.
Anyway, am I exaggerating, or do you think this is a valid issue ?!
By the way, who else would like to watch the fictional Cdrama, The Hidden Flower in My Garden ?! 
it didn’t happen before (or somehow I didn’t notice it?), why are they doing this to us 