...the market is only so large. So other camera makers need to think hard about whether they can compete against cameras made by Olympus and Panasonic.
Unless they are planning a one off alternative budge priced entry level camera, like Kodak did in 2012 and YI did in 2016, there really isn't much market potential for them.
Lens makers, on the other hand, rarely design lenses specifically for the Four Thirds sensor. Instead, they simply modify lenses designed for APSC or Full Frame by adding a M4/3 lens mount. And this costs them very little, and opens up an additional market for them.
This could explain why only two other camera makers (Kodak and YI) have made M4/3 camera bodies, and both have had very limited success with them.... but over a dozen lens makers have sold lenses with M4/3 lens mounts. With more joining the group every day.
According to the Dpreview product database, there have been 55 M4/3 camera bodies:
- 30 from Panasonic
- 23 from Olympus
- 1 from Kodak
- 1 from YI
.. and 117 M4/3 lenses
- 37 from Panasonic
- 31 from Olympus
- 11 from Samyang
- 11 from Rokinon (probably the same lenses as Samyang)
- 8 from Sigma
- 5 from Voigtlander
- 3 from Hartblei
- 3 from 7artisans
- 2 from Kamlan
- 2 from Lensbaby
- 2 from Venus Optics
- 1 from Tamron
- 1 from Tokina
plus dozens more Cine lenses that were modified with a M4/3 lens mount, that Dpreview doesn't put into their database. These are very high end lenses that are primarily aimed at Panasonic GH users who are videographers.
There just isn't much potential in competing against Olympus and Panasonic for camera bodies, but there is plenty of opportunity to sell M4/3 lenses that are faster, cheaper, or some focal length or type not yet offered by Panasonic or Olympus.