Big companies buy Bitcoin because they think it’ll go up in value over time. It’s digital gold, limited & not controlled by any government. Some also use it to protect against inflation or to look modern & forward thinking. It can also help boost their stock price if Bitcoin does well.
I agree with you Bitcoin is used as a store of value against fiat currency debasement, like digital gold, companies invest to diversify cash reserves, especially in a low_interest rate environment.