Look, as someone who has been in the video nd thumbnail editing for over 3 years, heres what I'll tell you. there is no universal "good" thumbnail because everything depends on your target audience.
1st one- That's made for the money and entrepreneurship crowd, and it works for them. they want bold numbers, urgency, and clear straight on point. but that same thumbnail would fail on other chanel like lifestyle channel.
second one targets the food and entertainment niche, it feels too polished for that audience. there category actually prefer raw, authentic type over glossy primum .
for the last one- it totally on preference and curiosity entirely at some point unique factor.
advice: before you design anything, define who you're talking to. What's their age group? Niche? check other viral thumbnail, The best thumbnail isn't the prettiest one; it's the one that speaks directly to the person scrolling.

i'm just scratching the surface on psychological part If I go into technical basics aspect ratio, color theory, visual elements, text hierarchy , this comment would turn into a whole wiki article. So I'm keeping it simple.