Why Is Early Exercise Generally Not Optimal for an American Call Option on a Non-Dividend-Paying Asset?

For a non-dividend-paying asset, such as most cryptocurrencies, an American call option's value is always greater if it is held, not exercised. Exercising early gives up the remaining time value, which is a potential source of future profit.

The holder can always sell the option for its intrinsic value plus time value, which is more than the intrinsic value gained by exercising.