Speaking only from experience with Japanese gf's, one of their main reasons is due to public baths. Over here in the states, they've preferred the "convenience" of a trimmed style, but whenever she or both of us visit Japan she needs to let it grow back to a "respectable" length which means no trimming for a couple of months in advance.
For each visit to Japan, at least a couple of small vacation trips are made to distant areas and most hotels/inns have communal baths or onsens where she would go in with her mother.
For each visit to Japan, at least a couple of small vacation trips are made to distant areas and most hotels/inns have communal baths or onsens where she would go in with her mother.