Prime Flash (and Prime pricing info on product tiles in stores, What's New, etc) are only shown to Prime members. Both Prime and non-Prime members see the Prime price on Product store pages, as there's more room to display it.

Because I'm a Prime member, they show fine for me:

I totally understand your confusion though, and there's definitely a case to be made to show the Prime Flash and Prime pricing information for all users. It's something that I'll suggest to the team. 

Please let me know if this helps? Or if you have any other questions/concerns?

Thanks for reaching out,

Laura