Refusal of assent was really rarely necessary. British monarchs still tended to wield real power up through George III, they just didn’t wield it with a heavy club after Charles I’s unfortunate end. It usually wasn’t necessary to withhold assent because up until the late 18th century the Prime Minister had to have the legitimate support of Parliament and the monarch. Today the monarch invites the PM to form a government in her name. In the past, that asking was not compulsory–legally, politically, culturally or etc. It’d be a constitutional crisis if QEII didn’t ask the next person to attain a majority in Parliament to form a government, but 200+ years ago it was common for the monarch to do just that. During George III’s reign he had several Prime Ministers who lost support in the commons. And he was recalcitrant when the proposed replacements were personally objectionable to them. In the case of Lord North he actually bullied him to remain on as PM even when he lacked ability in Parliament to get many bills through (a situation that would result in resignation today for the PM.) When the monarch has more direct control over the Prime Minister, withholding royal assent just isn’t necessary.
George I/II/III weren’t all that active as monarchs, and Britain was “mostly” a democratic-leaning constitutional monarchy in their reigns. But the monarch still had some legitimate political power, it was only a couple generations later when they had virtually none, and then a few generations later they were actually expected to have no involvement in politics at all.
