And shock you or destroy your equipment. A lot of what makes real (UL/ETL listed) chargers expensive is making sure that line voltage stays adequately separated from the low voltage side.
But that then leads onto the whole fake component issue. For example the component will be a optocoupler but the dirt cheap knock off supply may not be using the same level of quality or a knock off component as those found in genuine power supplies which _could_ create a High to Low voltage path if that part failed.
Even a very cheap and simplified design can do that. I wouldn't say "a lot" at all, maybe a few percent of the cost at most. It's a corner that could possibly be cut, but it's not one of the bigger corners.