

A lot of things can go wrong. A company can take the free code, change it slightly to work only with a proprietary file type and then use their resources to promote their version and make their proprietary filetype and proprietary program the industry standard. Unfortunately this sounds too familiar. There are even cases that the filetype is an open standard but obfuscated to make it impossible for anyone (including the original FOSS) to open/save it.

This is a very valid reason, indeed.