They also offer optional E2E encryption of synced vaults, such that you can only open them with your local password. Of course we can't know for sure that they're not peeking at the data, but it all seems above-board and I don't think it makes any sense to try and have that as a business model.
The same reason companies contribute to FOSS projects and various charity efforts? Despite what many people believe, companies are not forced to make money at all costs.