One of the biggest qualities North American furs had was a simple one: they were there to use in the first place. One of the largest sources of supply for European furs before 1492 was in northern Russia, flowing into Western Europe primarily via Novgorodian and later Russian traders through the Baltic. This region had been massively depleted by the 1500’s due to intense cultivation over a prolonged period, with the beaver in particular practically vanishing from Europe.

This factor was paired with an environmental phenomenon known as the Little Ice Age, which was a period of generally lower temperatures across the globe from around the 15th to the 19th centuries. I’m sure an environmental historian could speak more on this but the decline in temperature was certainly significant and had a broad historical impact: one the one hand, you could enjoy a winter fair on the frozen Thames, but if you were a Chinese peasant, famines caused by the temperature drop would (arguably) lead to the overthrow of your ruling dynasty by Jurchen tribes. Colder temperatures would undoubtedly cause an increase in desire for furs due to its excellent protective properties. In essence It was a classic low supply/high demand scenario that led to a boom in the transatlantic fur trade being as profitable as it was, with a relatively untapped source of supply sitting abundantly in North America.

While agreeing with the above comment. There were several other factors in their favor e.g.

• It a source for a number of Western European countries that had previously drawn on Eastern supplies. Which difficult and expensive including often via several intermediaries and often political complications. While the new American were just (though recognizing it often difficult) a sea voyage away and often from their own colonies. Which they were keen both to encourage and profit from.
• 'Comparatively' numerous and little valued by the native peoples. Who also much sought European goods. They were notably easily obtained and cheaper than than Eastern furs. Giving them a usually clear undercutting commercial advantage.
• Fashion, though difficult to grasp, not to be discounted. In this case the rise of the Beaver fur hat - for which Beaver fur made the best felt e.g. 1750 45% of British fur exports, worth £263,000 were of fur hats to Spain (these visible in Spanish paintings of the period).