When you buy an asset you do it because it provides yield, security, and capital gains. This is why people buy gold, real estate, and stocks. Bitcoin is one of the best-performing assets in financial history appreciating 100% plus a year on average.

Bitcoin is also very liquid, you can sell your BTC in seconds and get your dollars back. Nothing is more liquid than bitcoin apart from cash.

Tether is a different animal, it is a stable coin pegged to the dollar and there are some doubts about the amount of cash they held in reserve. Nothing to do with Bitcoin.

When you buy gold or real estate, you get to hold the asset but you don´t get also the equivalent amount in cash. That wouldn't make sense. When you want to sell it you do so at the market price. Exactly the same with Bitcoin.

Grayscale owns 600,000 BTC, Microstrategy 125,000, Tesla 40,000 Why do they do it? Because they know is the best investment ever.