Från LotR wiki :
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).
Med andra ord tills staden Smaug hade gett ett mycket bra försvar mot nästan alla slags attacker. Stadsbefolkningen levde i rädsla för invasion eller under något riktigt hot och kände sig så säker.
Det är inte värt någonting följande från wikien också:
...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...
Med andra ord, när de insåg deras problem, försökte många att lämna platsen för att överleva.
Slutligen, när det gäller ombyggnaden av staden efter dess decimering av 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.
Det här sista steget innebar att de inte behövde oroa sig för omlokalisering igen efter Smaugs död.
Dessutom innehåller @ invalid_iqs svar några utmärkta ekonomiska skäl till varför medborgarna var kvar.