the"를 왜 넣어야 하는지 아직도 모르겠어요 ㅠㅠ

I understand the frustration, and to your point, "I went to hospital" is almost always understood in context. But the distinction between "go to hospital" (as a patient) and "go to the hospital" (as a visitor, employee, or for any other reason) exists in British English, and in American English, "go to the hospital" is the default for any visit. Dropping the article loses that nuance, and in formal writing, it flags you as a non-native speaker even when the meaning is clear. Correct it once in your mental grammar and it stops being a struggle.