Because there's nothing stopping them spinning.
It means done without ceasing, without stopping; continuously.
The current Guinness World Record for the longest time jumping rope without stopping is 30 hours and 40 minutes.
stopping
Without stopping to think, he pulled the dog away from the oncoming car.
* * *
Nonstop is an adjective that describes something that continues without stopping or pausing.
sneeaae
Cardiac
25
Stopping it dead -in other words, stopping it without allowing it to run down.
10000km