/s (I feel dirty just for typing the above.)
The streaming at 128kbps IMO has always been an anti-piracy measure; given that those previews are inevitably going to be scraped, make them just teasers rather than the real thing, and encourage purchase (or the cancer that is "Repost and Follow this random irrelevant promotion network to download" ... which is another problem SoundCloud needs to solve).
It begs the question, though - with such a large engineering staff, why has SoundCloud always linked externally for "Buy" links rather than running its own store? It could capture a lot more of the value chain and lower friction-to-purchase for indie musicians. Perhaps the reason was to not be competitive with its initiatives to get record labels (who likely prefer to drive sales through existing platforms for quixotic reasons) on board for SoundCloud Go. But perhaps with new leadership and recalibration, this could actually happen. RIP Bandcamp though... or maybe they just acquire them!