1) The death of Ögedei Khan forced the hordes rampaging through Europe under Subutai to break off and return for the Kuraltai to choose a successor. Interrupting their hard-earned momentum, and giving the Europeans time to regroup, recover, reflect and prepare, was the deciding factor - also, Talabuga was not the general Subutai was.
2) Hungary is the end of the great Eurasian steppe - the "sea of grass" - that sustained Mongolian logistical supremacy. They were successful in the short term in pursuing conquests beyond this area - usually due to Chinese and Islamic engineering, the co-option of which was a significant factor in their success - but the setbacks they did encounter occurred away from the steppe, where reinforcements by the tens of thousands could be summoned in devastatingly short order. The Viet and Champa in their thick jungle, the Majapitt and their thalassocracy, the Mamluks in the desert hills - all of them counted geography as major allies. So it was with the Europeans who were even a little successful against the Mongols.
3) Some of the Europeans adapted faster than others against their Mongolian opponents. The Georgians almost beat them, the Croatians and then the Serbians did beat them (tho not decisively, and Serbia did acknowledge suzerainty of the Mongols to stop them from coming back) - Bela IV of Hungary, and his grandson, Ladislaus IV, took what worked, and built a successful strategy to repel the Golden Horde when they returned.
Innumerable stone castles in very defensible locations, well stocked and garrisoned with trained and equipped forces, capable of supporting each other.
A scorched-earth strategy, denying the invading armies of provender and supply.
Harrying tactics borrowed from the Cumans, steppe horse-archers similar to the Mongols that Ladislaus IV had defeated prior to the Golden Horde's arrival.
The Mongols could loot at will, but were constantly under attack. The Hungarians refused to give them a decisive battle, until the invaders were weakened and depleted and in conditions favorable to the defenders, who were wise to Mongolian battle tactics thanks to the influence of the Cumans.
And what could be more European than the Fabian strategy?