Not true. For example, mesh technology Thread is built on 802.15.4 and is very much multi-vendor. At least 4 companies make Thread chipsets (Silicon Labs, NXP, Qualcom, Nordic Semiconductor) and has 100+ member companies: https://www.threadgroup.org/thread-group#OurMembers There is an open source implementation from Google (OpenThread) who is a major member. Adoption and interest is really ramping up rapidly. Recently the spec was made freely and openly available. No royalties. I think it's really promising.
Disclosure: I participated a little bit in the design of Thread by doing a security review on behalf of Google.