I understand that spiking the football is a time management technique in American football, but I don't understand why there is no penalty (e.g. intentional grounding) associated with it?
This is actually a special rule case.
Section 2 Intentional Grounding
So you may spike the ball to stop the clock if you do so immediately after receiving the ball. However:
Thus waiting to do so is considered intentional grounding.
Because it's specifically permitted by the intentional grounding rule.
Rule 8, section 2, article 1 of the NFL Rules:
The NCAA has a similar rule (rule 7, section 3, article 2 of the NCAA rules):
So spiking is legal only if the snap was not fumbled, unlike the NFL.