Text boxes don't look like text boxes. Buttons don't look like buttons. Checked toggles might be easily confused with unchecked. Toggles also look like something you should drag, but do nothing unless you click them. Unchecked check-boxes look like oversized bullets from a bullet list.
Moreover, most controls are not semantic and simply stop working if you disable JavaScript. (And no, I don't care whether you consider this issue relevant or not. Users of text browsers, screen-readers, some mobile browsers and people with JS blockers will consider it relevant.)
Moreover #2, these controls don't blend in with text at all. They will distract users from actual website content.
Moreover, most controls are not semantic and simply stop working if you disable JavaScript. (And no, I don't care whether you consider this issue relevant or not. Users of text browsers, screen-readers, some mobile browsers and people with JS blockers will consider it relevant.)
Moreover #2, these controls don't blend in with text at all. They will distract users from actual website content.