It is because large-scale manufacturing agreements need to be in place, testing showing relevant comparisons need to be in place, ect... Coates can do smaller volume in part numbers of hundreds locally here in the US, but bigger volume would need big scale manufacturing, aka China.
There are way more orders than can be handled at the moment... which is a good thing! Interest has never been higher, tying up the needed contracts to push manufacturing ahead is close. Cummins may play a multi-faceted role too, considering they have the means, interest (and possibly motive) to be a consumer, manufacturer, and/or supplier.
They would likely procure several heads for some trial buys, run them and see how they perform over a period of several months of high mileage. If it means new marketing strategies and advantages for them in multiple fields of application, they would chose increasingly larger control.