Because often a payout and money in your pocket is worth more to you than the years of uncertainty
If someone offers you cash today to buy something which either might go up or down in value, many people will take the cash
But if people are selling because it will go down in value, the buyers know that too and bid less. The traded price will always be (approximately) one that makes you indifferent to buy or sell.
But if people are selling because it will go down in value, the buyers know that too and bid less. The traded price will always be (approximately) one that makes you indifferent to buy or sell.