When do they sue?

I have a chargeoff against me recently from a credit card debt with a high balance. But no judgements yet. The last payment on my credit account was January 2014. When there is a chargeoff and a person cannot possibly make any payments or deals of any kind at this time, due to financial hardship, (but nevertheless understands that the debt is still legally owed), will the agency always try to sue for a judgement against them on the theory that in the future money may be available? And how long usually do they act to sue after the charge off: Months later, years later, 19 years later, etc? Is there any rhyme or reason to it?