I don't believe there are canon sources for why it was rebuilt.
It's pretty easy to see why though.
The original purpose of Dale was to act as a trading nexus between the Dwarves and Men. Having a friendly town of men nearby would appeal to the suspicious and clannish dwarves.
The desolation of Smaug was no doubt mainly a result of the destruction and lack of maintenance of irrigation channels and infrastructure from the River Running. That would be relatively easy to re-instate after the Dragon was disposed of. Once irrigated dry land farming was started, this would have provided a source of food for the region and encouraged local settlements along the River. Key crops would have included wheat, Shiraz type grapes, citrus farming and maybe limited rice production, similar to the agriculture around the Murray River in Australia.
Finally, the town is very strategic, protecting the flank of the Dwarves and making a siege of the mountain more difficult to undertake without first disposing of Dale. By contrast the settlement at Esgaroth is too far away to be strategically significant.
No doubt, the Dwarves provided suitable trade concessions and other inducements to secure such a valuable strategic resource. Good relations with Dale (and the Elves of Mirkwood) would have been a key foreign policy objective of the Dwarves, as Thorin realised belatedly before his death.