Contrary to popular belief, a scar isn't as strong as normal skin.
I quote from the source below:
"When sutures are removed, usually at the end of the first week, wound strength is approximately 10% of the strength of unwounded skin, but it increases rapidly over the next 4 weeks. This rate of increase then slows at approximately the third month after the original incision and then reaches a plateau at about 70 to 80% of the tensile strength of unwounded skin, which may persist for life."
Although there is more collagen than before, the collagen isn't so efficiently structured, and the skin's elastin fibres are not regenerated at all. The reason that the scar's tensile strength increases over the first few months is due to changes in the collagen there: there's increased its synthesis, an increase in its fibre size and intricate crosslinking of these fibres.
Source: Robbins Pathologic Basis of Disease - 6th edn., Kotran et al.