Just as the title says: Why are bonus tracks so common in japanese versions of a release?
According to a user on MetaFilter:
According to a friend who runs a small record label that occasionally does business in Japan: it's because it is invariably cheaper for Japanese buyers to import CDs rather than purchase them in their local record store. The extra tracks are there to provide an incentive for buying the domestic version. Without the extra tracks, Japanese retailers are reluctant to sell the CDs knowing that a large portion of the potential purchasers will simply be importing the product.
Another user adds:
In Japan, an import from Europe or the States sometimes is half what a domestic CD. The bonus tracks are to encourage Japanese to buy the Japanese edition. An import buyer I used to know in my record store days hypothesized more Japanese editions are sold to US OCD collectors than in Japan on some titles.
I recall that a similar tactic was also used for European releases in the 1990s, because it was cheaper for record shops to import US CDs.
This is a guess, but a reasonably educated one…
JASRAC, the Japanese equivalent of PRS/MCPS/PPL [idk the US equivalents if someone wants to edit those in] has traditionally been considerably more lax in what it considers 'legitimate for release' [I'm using these terms very loosely, I'm neither a lawyer nor publishing expert]
This could result in releases such as the Beatles "Unsurpassed Masters" series, which ran to about 14 CDs last time I bought one there; which was in effect an entire suite of Beatles outtakes & unreleased versions, unavailable in any other country at the time.
Most of the material was actually released world-wide in the past 10 years, but at the time would have simply been considered 'bootleg' anywhere else.
My extension to that premise is that the record company could 'legally' under JASRAC add extra tracks - unfinished tracks, early demo versions etc - without the artist's permission.