My experience is that the Beatport and Tidal catalogues are filled with complete tracks/versions.
On SoundCloud you simply don’t; likewise on Mixcloud. Let’s say you search for a specific track, it might be that the artist only puts a snippet on there and not the complete track.
Beatport is aimed at DJs, and is similar to the likes of Traxsource in that it’s EDM etc. rather than commercial chart tracks.
SoundCloud is more for unsigned artists to upload their tracks, or more often DJs illegally uploading their mixes of copyrighted material, or unlicensed “bootleg” remixes that they’ve knocked together.