Great question — answering as the UphillTech team:
Possible Explanation: Google may not show review stars for SABs because they lack a physical address, making it harder to verify reviews. Google has been restricting review snippets for certain business types, especially those using LocalBusiness schema without a storefront. If Google considers the schema "self-serving" (manipulative or untrustworthy), it might ignore it.
Full answer by Business Working: https://webmasters.stackexchange.com/a/146661 (CC BY-SA 4.0).
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