Do wiki do SdA :
Uniquely, of all of the towns, settlements, fortresses, and cities of Middle-earth, Lake-town utilized water as its defense. The Long Lake was also surrounded by towering cliffs and high mountains, all helpful natural barriers that had the potential to aid its defenders in a siege (such as the Easterling invasion of the North in TA 3018).
Em outras palavras, até que Smaug, a cidade, forneceu uma defesa muito boa contra quase todas as formas de ataque. Os habitantes da cidade não estavam vivendo com medo de invasão ou sob qualquer ameaça real e, portanto, se sentiam seguros.
Também não vale nada do seguinte no wiki:
...Smaug, livid with bestial fury, had winged his way to the town in the dead of night and promptly began to immolate the wooden matchwood structures there, materials that burst into flame at the slightest provocation. Its inhabitants realized all too late their predicament and while some, including most of the women and children, got away safely on boats, many perished in the maelstrom of fire that ensued. A brave company of spearmen and archers attempted, in vain, to shoot down the dragon, but were mostly immolated themselves. The town was wrecked by the dragon...
Em outras palavras, uma vez que eles perceberam sua situação, muitos tentaram deixar o lugar para sobreviver.
Finalmente, no que diz respeito à reconstrução da cidade após a sua dizimação por Smaug:
The inhabitants also learned a crucially important, but painful, lesson bought with the blood of loved ones: the town was built to be less susceptible to flame and its military was expanded. These lessons greatly aided it during the War of the Ring.
Este último passo significou que eles não precisaram se preocupar com a realocação depois da morte de Smaug.
Além disso, a resposta do @ invalid_iq fornece algumas excelentes razões econômicas pelas quais o povo da cidade permaneceu.