Focus groups often fall prey to social proof and group think issues. Also there is a lack of context and skin in the game. It is all well and good to talk about something in abstract, but much more informative when you see a behaviour or observe someone using a product in situ.
Focus groups provide tangible evidence of research and feel ‘researchy’
“People with an aversion to asking questions conflate focus groups and (ethnographic) user research — and use the weakness inherent in focus groups to dismiss all research. Or, they want to do research, but only if it looks like a focus group, because sitting around a table next to a two-way mirror feels science-y. You can’t deny the visceral satisfaction of otherwise useless research theatre.”
Ethnography is a better start for user research.
“User research should be ethnography. That is something that tells you how people actually behave in a particular context and why. Sometimes there is a relationship between expressed opinions and actual behaviours”
“How do you reach people who have so much competition for their attention and such well-honed abilities to ignore things? And how do you make sure that you are working for a realistic view of what those priorities are, instead of making assumptions or relying on wishful thinking?”
Source: Focus groups are worthless | Medium | Erika Hall, Sept 2015