A windowcleaner has stopped cleaning in my area and declared himself bankrupt - that's a new one on me 
Going bankrupt I understand. For some people it's the only way to get out of debt that has built up over time. As he was a window cleaner it's unlikely that it was a business bankruptcy as it's hard to build up serious business debts - especially if a sole trader. Indeed, if he didn't own his own house or his house was in negative equity, it's very unlikely it would be taken from him.
Stopping trading I don't get though. When going bankrupt your debts are wiped clean. Sometimes an order will be made to pay a certain amount each month for a while (sometimes a number of years) - especially if the receiver feels that you have manipulated financial data to suit your purpose. Therefore I could understand someone making it look like they have stopped trading (i.e. cooking their books) to reduce the liability of a bankruptcy order, but not to actually stop trading.
I think it's more likely that now his outgoings have been vastly reduced, he doesn't need to work so hard to keep up with the debt repayments so is working less.