An account that stops being paid does not stay with the original lender indefinitely. It moves through a sequence of stages, and each has different economics behind it.
Internal recovery comes first
The original lender attempts collection itself for a period, because it has the customer relationship and the best information about their circumstances.
During this stage the account is still being reported as delinquent rather than defaulted, and the lender generally retains discretion to arrange payment plans or freeze interest.
This is the stage where cooperation achieves the most, since the lender is comparing recovery against the cost of escalating rather than against a purchase price.
Default is an accounting event
After a defined period of non-payment, the lender formally defaults the account, which triggers reporting to credit reference agencies and often closes the facility.
The lender also writes down the balance in its own accounts, so the debt is no longer carried as a performing asset regardless of what is eventually recovered.
That write-down is what makes later settlement offers possible, because the lender is recovering against a value it has already reduced rather than against the full balance.
Agencies collect for a fee
An external agency working on commission does not own the debt and is paid a share of what it recovers, so its incentive is volume of contact.
Because the original creditor still owns the balance, the agency's authority to settle is limited to whatever mandate it has been given.
Accounts that produce nothing are returned and passed to another agency, which is why the same debt can generate contact from several different firms in succession.
Sale changes who is owed
Portfolios of defaulted accounts are eventually sold outright, typically for a small fraction of face value, and the purchaser becomes the creditor.
Because the buyer paid substantially less than the balance, it can accept a settlement well below the full amount and still profit, which is why offers often appear at this stage.
The purchaser inherits the original terms and cannot add charges the original agreement did not permit, and it must be able to evidence the debt if the borrower disputes it.
Time limits and rights apply throughout
Most jurisdictions set a period after which a debt can no longer be enforced through the courts, and acknowledging the debt or making a payment can restart that clock.
Rules also govern contact frequency, the information a collector must provide on request, and the treatment of people in demonstrable financial difficulty.
Because these protections and time limits differ substantially by jurisdiction and change over time, anyone facing enforcement should confirm the rules that apply where they live.