Why don't more recordings have soundstage outside of speakers

Because most speakers suck. 

The fundamental question I have is that if the original recording only mixes the soundstage within the speaker boundary, then can your system playback have a soundstage that is beyond the speakers?

Pragnmus, what are you talking about. I mention the delay. It is not as important for localization as relative volume. Studies have confirmed this and you can prove it to yourself with one control. The one that says "Balance"

With a system that really images you will have to make small adjustments in balance with most records. Like 0.5 dB or so. 

@sounds_real_audio , you are absolutely correct, most speaker do suck even the better ones. 

Andy2, You can by reflecting sound off the side walls. The reflected sound can throw instruments that are hard left or right beyond the speaker. This is a distortion and a sign of poor system/room management. This is not to say that the ambience in the recording can not seem to come from everywhere, it frequently does. The ambience is at a low level to start with and in the smaller rooms we listen in the reflected sound can compete with sound coming directly from the speakers creating the sensation of venue ambience. Very cool. 

Why don’t more recordings have soundstage outside of speakers

It’s more in how the recording was done, sure having nothing (obstructions) on the outside of speakers help also, get hold of Roger Waters "Amused to Death", it’s done in Q sound, and some of it comes from behind you, and the barking dog at the beginning the first shocker comes form your right shoulder.

What I was told by recording engineer if I remember right.
To get the image happening outside the speakers, you a get right channel only signal (say voice), and if to want it to seem like it’s outside the right speaker you add the same "but out of phase" right channel sound into the left channel", this then shifts it from the right only to outside right.

Cheers George