Why did the aspects give up their power?

[Abyssion]

Why?

Was it the lazy approach that.. oh we don't need it anymore???

There will ALWAYS be threats... they were given the power to watch over Azeroth... so why give it up? To become dumb mortals?

[Deleted]

To power up the Dragon Soul and stop Deathwing.

[Netherspark]

It was the only way to kill Deathwing.

[Kih]

To protect Azeroth from the guano-crazy giant hell-bent dragon o3o

[huth]

Because otherwise, they'd have died. They were going to lose their power one way or another and they chose the option that at least let them continue living.

[Venziir]

It was their destiny - the end.

[fps90]

They still have some power, they are just mortal now.

[Joeydivision82]

I thought it was pretty clear during Cataclysm. It's not like Blizzard left out something that important.

[Reyina]

To save the world...?

[ringpriest]

Because writing interesting, plausible stories about the demi-divine guardians of the world takes a good deal of talent and imagination. But writing about colored magic dragons can be done by any cheap hack.

[Blarglord69]

Yea they had to give up there power, to stop ol iron jaw,side question can they still turn into dragons?

[Trassk]

The dragonsoul worked as a device that absorbed the dragon aspects power into it. It was said so years ago in well of eternity saga, where deathwing fashioned it and asked the aspects to give a portion of there power, and it wasn't until a thousend years later when rhonin cut over the dragon soul that there powers were returned.
So, the only means to destroying deathwing was to focus all there power into a single shot cast from the dragonsoul, which obviously wiped out there powers.

[Butler to Baby Sloths]

Yea they had to give up there power, to stop ol iron jaw,side question can they still turn into dragons?

They are dragons, of course they can. But they cannot use their old powers (create life, change the course of time, create magic, make the earth do their bidding or control the emerald dream). They are also no longer immortal, although dragons do traditionally live much longer than any other creatures, and it isn't like they are physically powerless either.

[Albert the fish]

they had to end deathwing, also apparently they felt it was time for mortals to step up to bat and they couldn't/wouldn't do that with immortal dragon (demi)gods hanging around so they forced the issue.

why its all on mortal shoulders in an existence with immortal world guardians is beyond me, but damnit that's the storyline.

[Sorraxe]

Why?

Was it the lazy approach that.. oh we don't need it anymore???

There will ALWAYS be threats... they were given the power to watch over Azeroth... so why give it up? To become dumb mortals?

You need to read more about lore. You have Neltharion who created the Deom Soul aka Dragon Soul which he powered it up with powers of the aspect to defeat the Burning Legion. This time again we went back in time to get the D- soul again to be empowered by the power of the aspect . And the hiting blow was fired by Thrall him self.