All oleanders (no matter what species), if they are not planted in the right spot, will not have a very good smell, or they will not have one at all.
One of the most important things that you need to know about oleanders is that they really like sun.
The oleanders around my neighborhood that don't have a fragrance are all under big trees that provide lots of shade.
Oleanders are not shade plants.
One of the main reasons that oleanders are so popular around my neighborhood in CA is that we don't get lots of rain, and oleanders do not need much water, and here in California we do not get that much water. In other words, oleanders are good for xeriscaping. The plant Nerium is part of the subfamily Apocynoideae.