-snip-
Is it because that their government doesnt support digitalization of currencies?
Japan however, rarely uses Local Bitcoins to trade just like other Asian country (except China that has a huge population), trades in Exchange and Payment Processor internal trades are different story however.
Other possible reasons are: [1] there have been a more store/establishment-accepted digital coin in circulation (Monac***) in the country and Bitcoin is just one of their options.
[2] Yen costs a lot less than other Asian Counties and a way less in comparison to Dollars or Euro; to compete with trades done by other local fiat currencies, each Japanese LocalBitcoins user should spend more Yen to match the spent $ of just one American State.
[3] Most of them (including rest of Asia) are using Third-party wallet to send and Exchange to trade.
etc.