Casey Winters argues that whether/when a company needs a second product is NOT predicted by its business model category (consumer, B2B, marketplace, subscription) — that's "a total red herring." What actually predicts it is business- and market-specific: competitive intensity, the strength of the acquisition channel (network effects vs. SEO vs. virality), retention mechanics, monetization potential, market size/growth, and how natural the product adjacencies are.
He supports this with paired case studies of companies that look like the same business model but diverged sharply:
In each pair, the company that looked like it needed a second product less often ended up needing one more, or vice versa — and valuation didn't track who actually "won" at new-product development. The lesson: evaluate the individual business's acquisition/retention/monetization specifics, not its category label.