Betacoin difficulty adjustment algo is set up to have difficulty recalculation every 6 blocks. That is for keeping average block time on 4 min, and network adjustment is fast. As for jumping up and down - here are my thoughts:

70-80% of Betacoin miners are long permanent miners, and see long term future of Betacoin - they keep network stable above 400K difficulty, and every day the number of that long-term miners increasing.
Another 20-30% of miners just do not care about any cryptocoins, they usually switching their hardware on different coins according to coinwarz, marketcap & buy orders on exchanges with only purpose - to have fast profits from above average profitable mining & selling their fast mined coin.

P.S. You can look on other cryptocoins with not fast difficulty adjustment algo, explore their blockchains for the last couple of weeks and see that sometimes on that networks block time is >200% above normal time, and blockchains on that networks often stuck.