Maybe SCHs aren't very well understood by many doctors. When I had my first bleed, the on-call doctor didn't tell me much and just said to go on pelvic rest since bleeding in pregnancy is common, but still concerning. Then sent me home with miscarriage paperwork.
The second doctor (my actual doctor) just sort of shrugged her shoulders and said to be optimistic and hope I don't miscarry since there's nothing they can do. When I asked if I should stay on pelvic rest, she just said, "well, its up to you. If you think it'll help...".
She said she hasn't been told whether or not its helpful, so she can't recommend it one way or the other.
(A few weeks later, and her getting pissy with me...I switched doctors). (I saw a few more doctors due to bleeds and being told to go in, and each one said to remain on pelvic rest.)
Then I saw the specialist for my NT scan, and he was adamant that I remain on pelvic rest and he was happy to hear I kept on it, even though it was sort of/kind of/not really recommended.
When I started seeing my new normal doctor, she also said to remain on pelvic rest until further notice, and she would tell me when it was safe for me to come off. And she's still going to give me growth scans every 6-8 weeks until birth since they're concerned LO is a "huge" baby. lol I think they have my dates wrong. He's measuring perfect with when I ovulated, not my LMP.
Anyways...
I think some doctors are just not well versed in SCHs and don't know what to say. I personally think they should always err on the side of caution and recommend you be on pelvic rest. If its the least you can do, then do it. IMO.