Dead vs Died

[belly_ttt]

Why on English TV programmes, I hear people say something like:
"I thought John was dead!"
but not
"I thought John died"
?

[Soup]

Why do people say was dead instead of died?

Adjective: I thought John was dead. Describes John.
Verb: I thought John died. Describes what John did.
Participle: I thought John had died. Describes what John had done.