Question

Why are single bonds stronger than double?

Answer 1

You mean `"why are double bonds stronger than single?"`

Explanation:

The modern chemical bond is conceived to be a region of high electron density between two positively charged nuclei, such nucleus-nucleus repulsion is minimized and a net attractive force results. For a `C-C` single bond, this electron density is directly between the carbon nuclei. A double bond has (i) this electron density between the nuclei; and (ii) electron density above and below the plane of the single bond. This electron density results in a greater attractive force.

As a chemist, as a physical scientist, we should put some numbers to this argument. See this site for further discussion, and quantitative data.