If it's Google Flights' pricing cache being out of date then that's not an airline dark pattern
(Its also possible there is a website dark pattern designed to make an option to pay less by not choosing your seat really non-obvious: I've never booked with Delta)
The airline would say it's your fault for getting a quote from an aggregator rather than direct from them though
The airline would say it's your fault for getting a quote from an aggregator rather than direct from them though