I haven't read the full thread but it was mentioned a few times on the first page or two.
But you are wrong to say that couples who would be willing to do surrogacy wouldn't be approved for adoption - pursuing surrogacy, in itself, wouldn't be a barrier to being approved to adopt. Of course they may not be approved for any number of other reasons, which is why the 'they should just adopt' line is ridiculous.
But pursuing surrogacy, itself, is not going to lead to someone not being approved as an adopter. Social workers would want to know that surrogacy plans have been fully abandoned before considering adoption (they don't want applicants who are hedging their bets) and that the couple of have no lingering grieving to do for a biological child.
But if a couple, for example, initially wanted to have a child by surrogate, but decided (for whatever reason) that it wasn't the right course of them (e.g. cost) and then, a year later, applied to adopt their pursuing of surrogacy would almost certainly not affect them negatively. In the same way, if a couple had a child with a surrogate five years ago, and now want to apply to adopt a sibling for their first child, the fact that the first child was conceived through surrogacy would not affect their application significantly.