Why do some amplifiers throw a bigger soundstage than others?

Mapman is right because he exposed almost all factors..

i will add vibrations resonance control and the room/house electrical grid factors...

The main factor , save if the design of the gear is not very good, room acoustic controls... For sure it takes a good amplifier but it is one of many factors...

With the same relatively good amplifier i can transform completely the soundstage impression by modifying the room... I did it by the way... It is not an opinion but a fact...

My soundstage was filling completely the room around me and beside me with no sound coming from the speakers plane ...the main fact was not my choice of amplifier , even if the amplifier must be minimally good for sure otherwise nothing work well , but the main factors was acoustics understanding and disposition of many devices of all kind to do the job ( resonators, and others devices)

But atmasphere explained why some amplifier do a good job and are better than others for the soundstage and timbre...

At the end it will be acoustic room disposition though the main factor...

I like the way a seasoned amp maker put it:

Competently designed speakers can sound different from each other.

Competently designed amplifiers can sound different from each other, but less so.

Two things: lack of phase shift and aural effects having to do with the 2nd and 3rd harmonics, the latter of which can make an amp seem more detailed and spacious.

Thanks @atmasphere

The perception of a larger soundstage can be influenced by various factors, including the design and characteristics of the amplifier itself. Here are a few reasons why some amplifiers may be perceived to have a bigger soundstage:

1. Power and dynamics
2. Low distortion
3. Channel separation
4. Transient response
5. Room acoustics

Thanks @mapman

Isn’t it nice to get straightforward and technical answers rather than responses that it’s user-error or placebo effect? Lazy thinking which blames listeners first is so enervating.

+1 @hilde45 @atmasphere @mapman @mahgister

Thank you all for distilling things properly. These important factors are often overlooked and/or usurped by either hyperbole or oscilloscopes.

In the “everything matters” way of thinking, the only valid test setup is to use identical conditions for both DUTs, and to introduce nothing extra into the apparatus that isn’t required for critical listening…that means no ABX switches, disconnecting and reassembling hookups, etc., which takes time.  Critically matching playback level is known to be a necessity in assessing quality.  How many of us can recall the sound well enough to judge in light of these factors?  I am in agreement with Jasonbourne on this one…I also believe the preamp is more instrumental in establishing soundstage than the power amp is in my experience.