Presumably you should care because tether is (per the OP argument) pushing the value of the entire crypto ecosystem up and the Bitcoin price is a primary beneficiary of that.
As a long-term BTC holder my primary reason is protection against debasement. It is a volatile asset, historically with 50-80% drawdowns from time to time. But as long as I think it still serves as a hedge against debasement I am happy to hold a portion of my net worth it in.
Growing up, I have seen fiat go worthless twice in my life: once the government zeroed out previous money overnight, once it hyperinflated fiat by over 1000x in two years. An 80% temporary drop is peanuts compared to that.