Different lens mounts exist for both business and technical reasons.

From a business standpoint, a unique mount helps keep customers in a brand’s system. Once someone owns several lenses, switching camera brands becomes expensive, so sharing mounts is not usually in a manufacturer’s interest.

But it’s not only lock-in. Mount design affects what a camera system can do: mechanical and electronic communication, autofocus design, aperture control, physical size, and how much room engineers have for future features. Different companies prioritize different design goals, so they create mounts that fit their own technology choices rather than accept another company’s compromises.

History also matters. Brands often try to maintain compatibility within their own systems, so older lenses can still work on newer bodies. Sometimes, though, a company makes a clean break to support new technology, which can create a new mount that is not backward compatible with earlier lenses.

So the short answer is: different mounts persist because they help brands differentiate their systems, preserve customer loyalty, and support each company’s own technical roadmap and legacy compatibility decisions.