Maybe a polite way of expressing their "social reason" is —
They felt very, very unwelcomed.
Although, perhaps a bit more of a direct description is captured by what I paraphrased, from someone at a recent Bluesky conference, here (at this URL):
https://mastodon.social/@reiver/114208310829137604
That paraphrasing is about developers (rather than the Bluesky team), but — my understanding is, I think the Bluesky team also had the same feeling.