A single account held the resume, the contact list, the job search, the company research and the industry commentary. Bundling was the product. Employers advertised where candidates already had profiles, and candidates kept profiles where employers advertised, which is the loop that produced the scale LinkedIn still reports today at more than 1.2 billion members. Microsoft acquired the company in 2016, and the directory advantage has not been seriously challenged since.
The weakness of a bundle is that it is second-best at most of its parts. That did not matter while there was nowhere else to go.