To reiterate and clarify the point from my original comment, you need to ask why and to what effect spending is done. The population of the US is much older and much unhealthier today than it was in 1970 and healthcare is more expensive. So increased spending on healthcare doesn't necessarily prove an increase in commitment to serve the people and can instead simply be a result of rising costs.
Also that Wikipedia link you included conveniently doesn't start until the very late 70s just after the top rate saw a huge drop from the levels established in the post-depression era.
Lastly you need to factor in growing income inequality in these numbers. It is possible for the top tax bracket to collectively pay both a higher share of taxes in both percentage and absolute dollars while each individual person in that tax bracket sees their tax rate decrease.
Also that Wikipedia link you included conveniently doesn't start until the very late 70s just after the top rate saw a huge drop from the levels established in the post-depression era.
Lastly you need to factor in growing income inequality in these numbers. It is possible for the top tax bracket to collectively pay both a higher share of taxes in both percentage and absolute dollars while each individual person in that tax bracket sees their tax rate decrease.