I'm not convinced that shared ownership increases costs for those people who choose it. Geographically speaking, it always depends on where you are. That said, as you mentioned at the end of your question, it may not be the choice these people want to make.
Take the example of a couple expecting their second child, and who would have liked to have bought a single-family home with a certain number of bedrooms and a small backyard, but whose borrowing capacity doesn't allow them to do so. Under these conditions, these people may have to opt for something a little smaller—an apartment or a townhouse, for instance. This doesn't correspond to their first choice, which they might have made before October 17, 2016.