When items go to the Border Ethereal, they don't have to move.
DMG 48 says that every location on the material plane overlaps with the corresponding location on the border ethereal plane:
The Ethereal Plane is a misty, fog-bound dimension. Its "shores," called the Border Ethereal, overlap the Material Plane and the Inner Planes, so that every location on those planes has a corresponding location on the Ethereal Plane.
Therefore, if you're simply moving the chest from the material plane to its corresponding location in the Border Ethereal, there is no movement per se.
This interpretation is consistent with the Ghost's etherealness ability, which allows it to move freely between the two planes (MM 147):
The ghost enters the Ethereal Plane from the Material Plane, or vice versa. It is visible on the Material Plane while it is in the Border Ethereal, and vice versa, yet it can't affect or be affected by anything on the other plane.
Note that while doing so costs the ghost an action, it doesn't cost it any movement. Additionally, while it's technically on another plane of existence, the Glyph of Warding spell doesn't address different planes, so I suppose it doesn't apply.
Leomund's Secret Chest is unclear
It's clear that if you summon your chest to yourself while more than 10 feet away from its original location, your Glyph of Warding spell will end. However, the text of the spell is a bit ambiguous as to where exactly on the Ethereal Plane the chest goes when the spell is initially cast.
If it just enters the Border Ethereal at its current location, then your plan will work, but if it goes somewhere else, then it won't. Given that the text doesn't specify, this will have to be something you work out with your DM.
In 5th Edition, the primary source of information about both planes is the DMG. Since you're asking about 5th specifically, we'll avoid talking about earlier editions.
The Ethereal Plane is what connects the Prime Material Plane, where all elements are found, to the Elemental Planes, which serve as the sources of those elements. While in the Ethereal, you can perceive the Material Plane if you're close enough to it, a region known as the Border Ethereal. Think of the various planes of matter and energy as a sphere, with the Prime Material as the globes surface and the different Elemental Planes bobbing about inside it. A mirror image of the Prime Material serves as the Feywild, and the shadow the Prime Material Plane makes is the Plane of Shadow.
The Astral Plane, on the other hand, is a timeless void. Everything in existence (except, due to the weirdness of cosmology, the Inner Planes) is accessible from the Astral Plane. Unlike the Ethereal Plane, travel in the Astral Plane is tied directly to thought, and it is believed that intelligent creatures travel to portions of the Astral Plane as they sleep. Near the outer areas of the Astral Plane, itself an eyeboggling concept due to its infinite size, are the realms of the abstract where the gods live and souls travel upon death, the Outer Planes.
Your key takeaways:
The Ethereal Plane can look upon the closest plane. It is otherwise a foggy realm that connects the Inner Planes and the Material Plane. It's not true to think of the Inner Planes as inside the Material Plane and the Ethereal as the goo holding it all together, but it helps.
The Astral Plane is timeless, almost featureless, and is home to everything non-physical or beyond mortality. The Astral Plane is what the Ethereal Plane sits in, surrounded at a great distance by the Outer Planes.
Best Answer
It’s simply because anything that is present, but incorporeal, on the material plane by definition exists partly in the Border Ethereal. An entity like a ghost, that is tethered to the material plane but has an incorporeal portion, has that part in the plane that is — definitionally — where incorporeal parts of material plane entities exist.
That’s the role of the ethereal plane: being the transition plane between the material and everything else in the planar cosmos. It isn’t primarily the place where “raw materials are turned into the Prime Material”: it only happens to also be that because its foremost nature is being the medium through which the inner planes connect, in both directions.
By contrast, the astral is not adjacent to the material plane, so it’s not a candidate for ghosts’ incorporeal portions. Travelling to the astral plane “naturally” — without portals or spells that take you there — requires passing through the ethereal first. Ghosts are trapped in the border ethereal and can’t even reach the rest of the ethereal plane, because they can’t fully leave the material plane. They certainly can’t reach edge of the ethereal where it meets the astral, and its access to an afterlife in the outer planes.