And Bitcoin is pretty liquid, at the moment if you market sold $5m million dollars worth of bitcoin on bitstamp you'd drop the price by about 1% and bitstamp is by no means the largest exchange. Obviously not being quite as bone headed as making bulk market order would do better.
... now, how much VTI shares can you sell right now? None. The major equities markets are closed. When the markets are open, sure big equities indexes are very liquid, but many single stocks -- even fairly large ones it would be pretty hard to move $5m in an instant without crushing the price.
If you have $3000 in stocks and you want need $100 you can sell the stock and then buy it back on your next paycheck. But unless your account is over a certain size, you can only do this so many times in a specified period.
Since this restriction doesn't exist with crypto, you can sell and buy back the same crypto 1000 times in a day if you want to (and many bot operators do this)