Why don't more recordings have soundstage outside of speakers

@mahgister I meant averagely good acoustically which is not measurable but I think most would know what I meant. if you want to make everything sound like mystery and magic then go ahead, there are some basic acoustic principles that are worth trying before you turn to guesswork. I'm not even sure what 'an experimental fact in acoustic' actually means.

As others have said there is a sound engineering 'trick' in which you pan an instrument or sound hard to one side and then mix in the same track panned hard to the other side but 180˚ out of phase. At the mixing desk it pops the track right outside of the speakers and leaves lots of space in the centre of the mix... which is very handy in a lot of cases. The effect only really works on a stereo loudspeakers, it doesn't work on headphones and in mono the instrument or sound will be greatly attenuated as the out of phase signal is summed with the original. In most cases an engineer doesn't know how a track will be listened to (with the exception of vinyl) so effects like these are used pretty sparingly.
Many systems are able to render a soundstage wider than the speakers even when there are no 'tricks' like this in play... I enjoy a number of recordings made with a single stereo pair of microphones that have a huge soundstage. In my experience it's usually down to the recording and the loudspeakers. An average room is capable of a wide soundstage as long as there is enough distance between the loudspeaker and the side walls to avoid flutter echos. You can put absorbers at the first reflection points (imagine the wall is a mirror and you're looking at the reflection of your loudspeaker from your listening position) to tame the worst of these.

I find all the disdain for tricks and gimmicks quite amusing - the whole thing is a trick unless you summon your own string quartet every time you listen to music. But I guess you could say that there is a continuum of musical production from the simplest mono recording through multi-mic setups to completely electronic music production. Personally I don't draw a line where one side is right and the other is wrong.
I like the threads here that make me go away and check my thinking, so I put on Bill Evans - Sunday at the Village Vanguard. From the minimal information I can find this appears to have been recorded with a three mic setup straight onto two track... nearly as simple as you can get. Listening on both my nearfield monitors and main speakers the instruments themselves spread slightly wider than the speakers themselves, it is however the ambience which is completely enveloping and gives you the sense of space. I've taken care setting up my listening space but it's a long way from being acoustically optimal.

Great... it's a brilliant LP.

If all early reflections are well dampened it is physically impossible for sound to come from beyond the speaker without studio tricks

That’s quite a bold statement... what’s it based upon?.. happy to be educated if there’s some definitive research out there.
The studio tricks are just an exaggeration of an effect that exists in nature which is that if a source of noise is closer to one ear than the other then our brain is able to detect the phase difference to help identify the point in space from where the sound came. If these differences are recorded to the left and right channels they can be reproduced by the loudspeakers. From your listening position each ear can hear a bit of each channel so I agree you can’t expect a 360˚ holographic stereo image. But I also don’t see why the stereo image should be bounded between the speakers - if our brains only used relative amplitude to locate the sources of sounds then it would make sense, but it’s not that simple.

Mijostus - 

You ability to determine where a sound is coming from depends mostly on where the loudest sound in coming from and the delay between getting to one ear to the other.

You then go on to talk about relative amplitude and don't mention the delay again at any point in your thought experiment. If you listen to a binaural recording through headphones it is immediately apparent that there's more going on than just 'the left is louder so it must be over there'.

People talking about music - 
Tom Waits' Rain Dogs LP has a nice sound stage too.