Most things go through upheaval in spring, especially so in Japan.
For one thing, people don't get as much sleep. First, there are the nendomatsu (year's end) obligations in March that triple the normal workload, especially for bureaucrats scrambling to meet the deadline for the section's budget or closing and renewing projects with clients.
Then there's the sobetsukai (farewell parties), thrown for those leaving their current posts and moving on to others; there's also ohanami (cherry-blossom viewing or, to put it bluntly, sitting under cherry trees on blue tarpaulin sheets and drinking oneself into oblivion); and finally the various kansogeikai (welcoming new employees and respectfully ushering out retirees and/or those leaving the workplace) that fill up the social calendar well into the second week of April.