I find it is quite common that helpers change job frequently - they make more $$ by not performing. One month in lieu + encashment of air ticket + leave entitlement in lieu... Many of them get $5k+.
If a helper is terminated 2 times a year, she get extra $10k+. This is an extra amount she won't be able to get if she works well in one family. They have nothing to lose.
What is the motivation to work?
The government should take some measures - for example, complusory repatriation to home country for those premature termination; 12-24 months suspension of visa application for those with 2 or more premature termination in 2 years time. This would to some extent increase their cost of breaking contract.