I don't know about the thinking of others but IMHO the scalpel blades are simply a generally more usable shape. The scalpel blades have enough of a point to allow fine work and poking holes and enough curvature to allow them to be used to scrape a skin or perform similar tasks without the corners catching and poking holes.

Then again I usually tend to prefer to slip in a tiny, but good quality, pocketknife rather than worry about raw blades like scalpel or razor blades. A pocket knife has a handle, I have sliced myself pretty well using a razor blade, and integral sheath attached which makes them a lot handier and safer to use. Even a small pocket knife is a lot tougher than the bare blades, which tend to snap with fairly slight lateral pressure.

About the only thing that the bare blades have going for them is that they are very compact, light and sharp. They and will hide in a belt, wallet or buried in the sole of a shoe and they are literally shaving sharp.