Does a roof with 3 layers of asphalt shingles somehow last longer?
No. Layers of shingles on top of each other shorten the life of the roof due to the newest layer sitting on an uneven lower surfaces. 

The best life will come from removing all the old layers down to roof boards or sheathing and then laying down the new roof on a well repaired flat surface.

Multiple layers of shingles happen because folks want to avoid extra removal work or to save the cost of removal labor and disposal costs. There is basically no truth to claims of benefits of stacking shingle layers.