1. There aren't the tangible milestones that there are in baseball (bases, strikes, balls, outs) and football (yards, downs). Sure there are passes, position, etc. But a midfielder passing it to another one doesn't give the sense of jeopardy that "runner on second, 2 outs, 3 balls no strikes" or "second and 5 on the 25 yard line" give. American audiences that understand those implications are willing to wait up to 25 seconds between action to see how the next play impacts the situation.

2. Americans are used to pauses between plays to build suspense and provide other stimulation of the audience senses while they wait, such as commercials and competitions at the stadium.

You don't wait 25 seconds between passes of the soccer ball. It's continual buildup, letdown, and buildup again. You also don't get the quick stimulation of the senses from commercials and distractions at the stadium that are so common in the big 3 US sports. Though soccer fans at the stadium do create their own strange brand of entertainment.