The reason why butter shouldn't be refrigerated is because butter has a high fat content, which is often over 80 percent and low water content, along with pasteurization that make the butter resistant to bacterial growth, and the salt in salted butter also acts as a natural preservative, which keeps the butter safe at room temperature for days or even weeks.
Although the butter can still become rancid over time, and affect quality but not safety.
Butter is also easier to spread when it's kept at room temperature, although in hot weather and hot rooms, the butter can melt and go bad faster so it hot weather or hot rooms, it's better to refrigerate the butter.
The reason why Europeans don't refrigerate butter is because European butter often has a higher fat content and less water and is also often salted, which makes the European butter more naturally resistant to spoilage and keeping it soft for easy spreading.
Keeping the European butter soft for easy spreading is also a key preference for fresh bread, and they use covered dishes or butter bells also known as crocks to protect their butter from air and light, although in very hot climates, the European butter may still need refrigeration.
European style butter often has 82% to 86% butterfat when compared to American butter which often has 80% butterfat, which also means less water for microbes to thrive in.
The salt added to European butter also acts as a natural preservative for the butter, especially in salted or demi-sel butter, which extends the shelf life of European utter.
And keeping the butter soft at around 60 F by not refrigerating the butter also makes the butter much easier to spread on bread, which is a common practice in many European households.
Europeans also use butter bells or covered dishes for their butter, which also creates an airtight seal, using water in the butter bells base, or shield the butter from oxygen and light, preventing rancidity of the butter.
But in warm and hot climates, the butter can still melt and spoil faster, so refrigeration is necessary even for European butter in warm and hot weather.
And for storing the butter for months, the freezer is best, the fridge works best for keeping the butter for weeks to a couple of months but freezing butter can make it last longer and can even last up to a year or longer when frozen.
Cold butter is also essential in recipes like pie crusts and flaky pastries.