> Isn't it difficult to adapt to left-side driving while having used to right-side?

You get used to it after a few minutes. It takes a bit more concentration, especially when turning out of one-way streets, but it's otherwise fine.

There are mutual recognition agreements between many pairs of countries. The UK, for example, will allow you to directly exchange a licence from an EU or EEA, a British Crown Dependency, or a 'designated country' (Andorra, Australia, Barbados, British Virgin Islands, Canada, Cayman Islands, Falkland Islands, Faroe Islands, Gibraltar, Hong Kong, Japan, Moldova, Monaco, New Zealand, Republic of Korea, Republic of North Macedonia, Singapore, South Africa, Switzerland, Taiwan, Ukraine, United Arab Emirates and Zimbabwe) for a British licence with no need for a retest. Most of those countries drive on the 'wrong' side of the road.

The hardest part of learning to drive on the left is not turning on your windshield wipers every time you turn a corner.

Really though, the actual driving part is pretty easy to pick up. You get accustommed to it quickly. You're more likely to have problems crossing the street on foot (you'll look the wrong way for traffic) than driving.

I've driven in many countries including some pretty crazy ones and ones that drive on the wrong side of the road. You adjust/adapt ;) Every now and then though I still turned on the windshield wipers instead of signalling... And when the roads were completely empty you sometimes don't think and almost turn into the wrong lane... And roundabouts are also fun, like driving in Paris with their crazy multi-lane roundabouts.

The funny thing is e.g. in Canada, if you move there from certain countries, you can drive for 6 months on your foreign license, but then you have to take a road test to get a Canadian license!

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.

Contrary to the sibling commenters, I found this pretty tricky to do; I was always too close to the curb or the lane marker, I lost my natural sense of where my car was positioned on the road. I have the same general surprise that you can just use a US license to drive in Europe --- but you can. The IDP seems pretty silly, especially knowing what little it takes to pick one up.

Although it wouldn't have helped in that situation, as the Polish don't need IDPs in Ireland.