Cost is only part of it..
Weight.. a good quality well made hardwood handle with properly oriented grain is going to be hands down stronger than a steel one, *PER POUND*. Every ounce counts if you are working that shovel, pickaxe, etc for hours..
A wood handle also transmits less shock; really noticeable with something like a splitting maul.
A steel handle is a misery in cold weather.
Of
course, if the choice is garbage quality wood, steel will win every time...
A lot of the tools in the hardware store here have visibly flawed handles; take a couple minutes, look at the grain, and pick the ones that won't break on the first usage..
And don't let anyone else use your good shovel, fools are always confusing them for prybars. Steel handled shovels are perfect for friends or WWOOFers..
Seems around here with modern tools the steel is just as suspect; can't really tell if it's ok by looking like you can the wood, and pot-metal mattocks don't last long..