"Why do you want to join us?" seems soft but it's a real filter: companies want people who chose them specifically, because those people stay and contribute more. The failure modes are generic ("you're a great company") and self-only ("the pay and the perks").

The formula: specific + genuine + two-way

A strong answer connects three things:

1. Something specific about the company — that you could only know by doing research.
2. Your own goals/strengths — why this is the right next step for you.
3. What you'd contribute — it's a mutual fit, not just you wanting in.

Where to find the specifics

• The product itself — use it. Have an informed opinion. "I tried your onboarding and noticed X."
• The engineering blog / tech talks — "I read your post on migrating to a monorepo / your rendering architecture — that's the kind of problem I want to work on."
• Scale / domain — "Working on something millions of people use changes how you think about performance and reliability — I want that bar."
• Mission — if it genuinely resonates, say why, concretely.
• Recent news — a launch, a funding round, a new market.

Example structure

"Three things. First, the product — I've used [X] and the [specific feature] is exactly the kind of polished, performance-sensitive frontend I care about. Second, the scale — I've worked on apps with thousands of users; I want to work at millions, where the performance and reliability problems get genuinely hard. Third, I read your engineering blog post on [Y], and that approach lines up with how I like to work. On my side, I bring [your relevant strength], which maps directly to [a need you can see they have]."

What to avoid

• Generic flattery — "you're an industry leader, great culture." Could be said to anyone.
• Comp/perks as the headline — fine to care about, bad to lead with.
• "I need a job" energy — even if true.
• Getting facts wrong — worse than being vague. Verify your research.

What interviewers want to hear

• You did the homework — specifics prove it.
• Your motivation is durable (product/problems/growth), not transactional (perks).
• You see it as a fit, with something to give, not just to get.

Senior framing

At senior level, this also signals judgment about your own career. A thoughtful "why us" — tied to the technical problems you want to solve and the impact you want to have — shows you're choosing deliberately, which correlates with retention and engagement. Do the research; one specific, accurate detail beats five generic compliments.