why do people say sound doesnt travel in space?

Because sound needs a medium, of a minimum density, to propagate, space is so close to a vacuum that sound will not propagate.

You are asking us a question about "why people say..." There are many reasons, its a foolish question.

The ones I care to list are:

They make the claim without knowing anything about the actual situation.

They are ignorant and are simply repeating something they have heard as fact.

They know what they are talking about and choose to define the term "sound" to exclude the density waves which do indeed occur in space.

They actually hold that sound does travel in space, but believe the least misleading "sound-byte" answer to a lay question is that it doesn't

They actually hold that sound does travel in space, but believe the actual technical answer is inappropriate for the general public.

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Sound is the compression and expansion of a fluid (gas, liquid or plasma).

If we want to restrict ourselves to audible sound, then there is almost nothing in outer space which is capable of creating a pressure wave with sufficient intensity for us to hear (assuming we built special ear coverings which would allow vibrations to be transferred from the vacuum to our eardrums.

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I argue that pressure (more appropriately termed "density") waves not only created the Solar System and the Earth and Sun, but created the nebulae in the space pictures that are so astonishing to look at.

In addition, since the solar wind blows out of the Sun and varies due to magnetic and electrical fields, I argue that with the right instruments we can hear the Solar Wind blow.

And lest we forget, consider the Van Allen belt and the auroras.

Sound doesn't travel in a vacuum. What we perceive as sound are actually tiny pressure waves travelling through a medium (like air or water or rock).

There is no medium that the sound waves can propagate through in space.

If you hit a nail with a hammer, or you smash a glass, or you fire a gun, no sound waves are created.

There is no sound in space. Sound is of course a wave - but it is a wave through air - or water or even solid material. Without an ambient medium to transmit the energy from the hammer blow there is no sound radiating from it.

Imagine a line of dominoes standing up on a table. You knock one down by disturbing it and it knocks over the next one and that knocks over the next and so forth. But if you had one domino (or the dominoes were too far apart) then knocking over one does not transmit the 'wave' of falling dominoes through the medium of dominoes. So that is sort of how sound works. The initial disturbance pushes adjacent air molecules, which push on the next, which push on the next in a pressure wave that propagates as long as there is energy left and air molecules to be disturbed. In space there is nothing to disturb. So striking the hammer is like knocking over a single domino.

"Sound waves" occur in air when there is atmosphere. There is no atmosphere in space. So there are really no atoms to compress between the hammer and nail, or are up against the board when the hammer lands, to be differently displaced.

Sound only travels through particles which space seek to have

There's no atmosphere through which the sound waves can travel.

sound uses air to move there is no air in space therefore there is no sound

sound travels thru the air in vibrations

in space there is no air its a vacuum so it really has nothing to travel thru so you wouldn't hear sound in space

...Space is a complete vacuum and void of the reflective attributes needed to carry "sound".