Realistically the answer is probably that countries accept a certain risk of collisions in the interest of good international relations and the resulting tourism and business. They might also trust visitors to pay more attention. There are rules that attempt to restrict the abuse of IDPs (e.g. available for a max period of 1 year and only available in your home country, and in some countries it may be illegal for people on longer-term visa statuses to use them), but it's all tradeoffs. I can imagine that e.g. Uber might be lobbying politicians to make them less widely available, and they may succeed.