Another way to view a soul is as a soul, like the one in a mage. When using an enchanted item, you are not converting the soul into magical energy, but are drawing on the soul's magicka reserves. The soul would recover its magika as a mage would, with rest. As it is, Morrowind's enchantments work one way, and Oblivion's and Skyrim's work another. The way magic is practiced in Oblivion, maybe Soul Trap fails to capture the entire soul, and snatches only the soul's pool of magicka. Maybe the entire soul is captured, but the art of enchanting as practiced in Cyrodil and in Skyrim is defective, and the soul is actually converted to energy, or leaks out with its magicka.
Well more like having entrapped soul thats still has personality is defective and was purified during better magic researching, since before soul trap was Mysticism spell it was not completely explored and understand in mechanic and then Enchanters found way use pure energy of souls.
For example Daggerfall has
Disadvantage Soul Bond thats as all disadvantages shift item limits in enchanting and allow more powerful enchanting created but in cost of certain Disadvantage.
The more powerful of a creature, the more powerful the item can be. Certain creatures have extra advantages and disadvantages forced upon you for using them to enchant your items. If your item breaks, then the creature is released, and will attack you.
For example Daedra Lord soul add additionally to player used enchant properties such features
Potent vs. Daedra, User takes damage in holy places, Extra Weight
So soul bond allow use more powers in cost of more sentient and willful soul thats can potentially rebel against master.
In Morrowind process of enchanting and soul trapping become more advanced, Enchanter found way to clean soul from it personality and leave only it soul power and ability to restore it magicka energy.
In Cyrodiil mages use only pure energy of soul without of any personality left, seems in Skyrim they will work in similar way, perhaps because their arcane knowledge now mostly based on remnants of knowledge from Mage Guild, what use more utility way to work with arcane energy then Telvanni Mystics and Enchanters what use more Old Ways of Arcane researching, thats also explain why they know more ways to enchant items and why constant enchants was more hard to achieve while Cyrodiilic mages make constant enchants accessible for all, in Cyrodiil enchanting is sort of crafting while in Daggerfall and Morrowind it also has some ritualistic and arcane mysticism.
Well I understood why they use Oblivion style enchanting from gameplay purposes also its limitation from creating uber items, balancing economy since Soul Gems can cost now and be more rare so and magical items will become more valuable while inability create own spells and requirement break enchanted items to learn it spell effects instead of easy purchasing of spells for enchanting, will move economy and exploration also.
But why such nice features like certain Advantages and Disadvantages from Daggerfall and slow enchanting regenerations will work awesome as some middle and high levels perks, while charge usage decrease with leveling of enchanting skills work awesome as good reason level enchanting skill.
Why not use it?
Easy achievable constant enchants return also in Skyrim, so my hope on cast on use enchants decrease, why limit ways of use our creativity in such manner, cast on use have only few problems (100 success chance and no casting delay such problems easy to fix) why decrease such features especially now when spellmaking is out for sure?
I hope Skyrim scripting system will powerful like OBSE so such features what devs don't want to implement by various reason will return with mods.