Perhaps Roku’s demographics skew older than Fire’s? If so, then I could see where political ads would tend towards Roku (since older people are much more likely to vote.) On the other hand, I believe many product advertisers don’t really target older people much. (Since older people don’t spend as much money and are perceived to be more locked into their brand choices.)
Oh, then again, I just googled up this page about what Ads Amazon accepts which includes bans on: “Political party-related and/or issue-related messages”. That is one weird list though. It also includes: “Adult incontinence products”, “Baby formula”, “Caregivers”, “Charities and non-profit organizations”, “Financial Services”, and “Free non-Kindle ebooks” (hah! Go figure!).
On the other hand, on this similar Roku page about ads, I see some overlaps with the Amazon guide lines such as: tobacco, “adult” products,… but I don’t see all those oddly specific limitations that the Amazon list has. Ie: no bans on politics, financial services, charities, and most of all – no ban on “Free non-Kindle ebooks”!! 😀 I suppose because of its size and clout, on FireTV, both the usual customer (advertiser) and Amazon are The Customer.