I think there may be Bible believing Christians who do believe Gap, but keep quiet about it for fear of rejection by their churches or other fellow Christians.
There absolutely are. Just as there are those who believe in evolution yet still maintain belief in Jesus death burial and resurrection- Dr Hugh Ross for example. The pastor of the Baptist church I used to go to for another example.
I just don't agree with them. For the reasons I shared, and many others that I didn't explain.
@mattfivefour brings up death and that is another reason. There are more.
You asked what people thought of the Genesis Gap theory. I explained what I believe and some of why. The logical inconsistency of needing a literal Adam and Eve, a literal fall that occurred before Eve was pregnant in order to need a Saviour, in order for God to supply His own Son, born of a Virgin. Very God and very man.
People don't think logically. Most people think emotionally and they understand their need for a Saviour on a deep level without realizing that makes no sense in a world that just evolved even if it evolved under benign neglect and occasional intervention by God as a lot of liberal minded Christians think.
They are still saved if they look to Christ's one and only sacrifice on the cross for God's payment of their debt.
They just don't understand the framework of that salvation or why Christ needed to be born of a virgin.
Sadly when kids grow up in these homes and go to university their professors are all too eager to point out logical inconsistencies and without understanding the faith on which they stand some crumble and fall away while others hold out their hope in Christ and grab onto the Gap theories.