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Is there any reason the various healing spells (for example, Elemental Spear [Water] and Grove Renewal) can't be used to revive the recently dead?

Because you cannot saw with a spoon?:P

In my opinion,

Death is a serious matter in Earthdawn. It is basically a horror-themed role-playing game. As such, death is death. With the exceptions of rare and powerful magics, there is no way of recovering from death.

Fourth Circle Magics, such as Elemental Spear - Water and Grove Renewal are not powerful enough to break the barrier of Death.

^^^ Pretty much this.

But death isn't death. You've got Last Chance Salves which, although Very Rare, cost "only" 600 silver (by comparison, non-magical plate armor runs 3000 silver, and Huntsman's Boots, which "keep the wearer’s feet both warm and dry" and let one "walk an additional five miles each day" costs 700 silver (and are "merely" Rare).

You've got Death Cheats which costs 450sp and give you a +6 to your Recovery test -- both Last Chance Salves (which can be applied hours after "death") and Death Cheats also give you a free Recovery if you lack them.

Basically, I see no functional difference between how things like Life Check and Last Chance Salves function and how spells like those mentioned function.

And if there is an unseen difference, how can something like a Last Chance Salve cost only 600 silver? There is a difference between "rare as in they are just hard to find, like a sword made specifically for windlings" and "rare as in hard to find because they are hard to make, being the product of incredible magics".

I have no comment as to why there are no "Last Chance Salve"-like (or other re-vivication) spell, but I did want to say that I suspect it'd be a Nethermancer spell.

Take a look at it this way.

In D&D 5th edition: If damage reduces you to 0 hit points and fails to kill you, you fall unconscious. At this point you begin making checks to see if you die.

In Earthdawn, they are two separate ratings, the point at which you fall unconscious (and can be heals with spells) and the point at which you die (and can't).

The fact that something is not expensive does not make it less powerful. I am sure many people in Earthdawn create Death Cheat Blood Charms and Last Chance Salves because many people want them. Supply and Demand. Many people buy them, so they are rare, Many people make them and sell them, so they tend to be cheap.

There is a "Last Chance Salve"-like spell called "Last Chance". It's a fourth circle Nethermancer spell.

It is perfectly legitimate to rule that Last Chance Salves are under-priced for your game and to increase the cost. But don't forget they are consumables, whereas the other items are not.