If Camellia is of equivalent security and speed to AES, concerns arise.

First of all, assuming the above, why is Camellia so rarely used in practice?
Why aren't there any breaks in Camellia? Does that mean that Camellia is currently more secure than AES, or is this a result of the lack of research on the cryptanalysis of the cipher?

There are a variety of reasons why AES is more widely used:


AES is a standard.
AES has been vetted by cryptanalysts more extensively than Camellia.  As a result, we can have greater confidence in the security of AES than in Camellia.  Therefore, on the merits, there may be good reasons to choose AES over Camellia.
AES is a government standard (FIPS).  Government procurements may be required to comply with applicable government standards.  Therefore, when selling to the government, AES may be required; if so, Camellia isn't an acceptable substitute.
AES is a industry standard.  No one will get fired for using AES. If (say) Apple uses AES, and AES gets broken, the newspaper headline won't be about Apple; it'll be about flaws in something everyone is using. On the other hand, if Apple uses Camellia and Camellia gets broken, the newspaper headline will be about why Apple took it upon themselves to deviate from industry standard practice and how that led to a security breach in their systems.  Therefore, aside from its merits, there's an incentive to choose the industry standard.
Camellia is patented.  AES is unpatented and free for all to use, without patent encumbrances.  Regardless of what licenses might be available, many people are a bit wary about any patented algorithm, due to uncertainty, IP risks, etc.  If the unencumbered version is every bit as good, it's easier to use the unencumbered version.  Also, it is possible that some open source crypto library developers may be less likely to implement Camellia, because of the potential patent situation or because of the reduced demand to the above factors, so standard crypto libraries are less likely to Camellia.  Similarly, many standards bodies have a bias against patent-encumbered algorithms, when there are alternatives that are every bit as good; therefore, some standards bodies may be less likely to use Camellia when they standardize on network protocols that require crypto.
AES is entrenched.  AES is a brand name that is widely known and recognized.  Also, AES is good enough.  Camellia is newer, and the benefits of Camellia are unclear or not as well known.  (In many contexts, Camellia has no obvious advantages, so a developer might not see any reason to adopt it instead of AES, if they already know and trust AES and consider AES adequate for their needs.)  There's no shortage of other block ciphers out there that could be considered, but if AES is good enough, there's not much incentive to use them.

