Beyond any SEO angle, there are several genuinely practical business reasons someone might reasonably want to acquire a domain that previously belonged to someone else.
Reclaiming a Brand's Own Former Domain
A business that once owned a domain and let it lapse, whether by accident or during a transition, may want to reclaim it directly.
Redirecting Traffic From an Acquired Business
When acquiring another company, taking over its expiring domain and redirecting it to your current site preserves existing traffic and links.
Building a New, Legitimate Site With a Head Start
A domain with genuine prior content and history can offer real advantages for a new, honestly built website in the same general subject area.
Next step: Use the Wayback Expired Domains to research a specific domain's history as you evaluate whether it fits a legitimate use case.