Why is it the people who are the most negative...

Isn't it obvious?

cause they are toxic and usually lose because of that. when they finally win a game they have to make it as spectacular as possible cause they will probably lose their match again.

Sometimes they're trying to provoke opponents into losing their cool and making more mistakes like challenging a fed opponent to prove themselves. Another exception is when they're dead and trying to distract opponents, though in those cases I find saying "I know what's hidden in your external hard drive" is way more effective than any trashtalk.