Well actually there is a way around that, but you are only interested in status quo.Part of the approvals for that project will have included various studies relating to traffic management and such. It's really common for the development of a subdivision to be required to install a signalized traffic controls at an intersection that's down the road. Or adding lanes to an existing road to handle more traffic. Etc.
Not really any different in effect than doubling the allowable density in an older neighborhood that was mapped in the 1900s and which has narrow streets which cannot readily accommodate twice the traffic and on-street parking. Either way they're adding to the traffic and parking situations. The same with urbanization along the existing traffic corridors - you're going to get more traffic overall. There's no way around that.
Adding to an already significant traffic problem, is just e plain stupid.
Developers putting traffic lights is not going to fix congestion. There's no space to put more lanes.
Pure lack of foresight or more likely just not giving a sh!t. It's all about the short term gain.