I think the one dose thing is interesting but it's a flawed presentation of data.
What age group likely contains the largest percentage of unvaccinated people? Most likely children and young adults a.k.a. the people least likely to die.
The people mostly likely to get vaccinated are the older people who can die from other causes quite easily.
I see the part that says under 50 but I don't see any graphs that show that in your screenshot. Provide the source please.