Indeed; in the UK, you need courier insurance to be a delivery driver. If you're just Joe Public doing Amazon deliveries, you are potentially driving without insurance.
If you're just Joe Public doing Amazon deliveries, you can also break the speed limit or park illegally in order to make your deliveries. How is that any different from not being properly insured? It's the courier's responsibility to not do those things. The most Amazon can do is to not work with people they know break the law.
Illegal parking is a civil offense, and you're not likely to speed enough to get banned, whereas driving without insurance is a pretty serious criminal offense and will make it much more expensive to get insurance in the future.