Because the speaker started to think like that at the moment in the past, and he/she is keeping that idea until now. 思いました in this sentence is not the simple past, but similar to the present perfect tense in English.
The Language Level symbol shows a user's proficiency in the languages they're interested in. Setting your Language Level helps other users provide you with answers that aren't too complex or too simple.
Has difficulty understanding even short answers in this language.
Can ask simple questions and can understand simple answers.
Can ask all types of general questions and can understand longer answers.
Can understand long, complex answers.
This answer was given within 60 minutes of the question being posted.
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