Sponsored Images only give BAT to users in the US / Canada regions; if you have your locale set to US and are not currently you will see Ads but not be rewarded for them.
That is the choice of the advertisers themselves. They choose which type(s) of ads they want to buy (notification, new-tab), and apparently there are no advertisers outside of the U.S. and Canada who are buying new-tab (sponsored image) ads.
@GreenBananaPorridge I don’t think that ntp Sponsored Images only give BATs to users in US/Canada region. I am in India. I see ntp Sponsored Images and get paid also. They are available in my region. See this-
You are right that if I set my location to US (say, through VPN), I will see Sponsored images but will not be rewarded for them.
@Dario89 Check https://sampson.codes/brave/ads/my_region/ to see if there are new tab page ads available in your region and to clear doubts. If there is a campaign with less than 24 hrs remaining you might not see that ad.
I also did not see sponsored images yesterday (whole day) as there was only one ntp campaign in my region with less than 24 hrs remaining (I had already seen ntp ads from that campaign). Its all good today.