Intuitively, the debtor seems to be the weaker party and to an extent it is but there is much more to debt (sovereign or not) than that. Obviously, creditors also profit from lending. Interestingly, countries sometimes actually borrow money at negative interest rates (taking inflation into account), which underlies how desperate some private actors are to lend money to them in turbulent times.

Also, it's tempting to see a trade surplus as a sign and source of power but it can actually result from a weak interior demand and an aging population (as in the case of Germany). By an accounting identity, trade surplus is necessary equal to net capital outflow. Since they do not consume or invest so much at home, Germans sorely need an outlet for all their savings (not necessarily sovereign debt but foreign debt in general) and profit from bubbles elsewhere (say US subprime lending or real estate in Spain before the crisis). They can't easily run from that without suffering severe consequences, both parties are caught in this game.

Incidentally, note that debt is being payed back constantly. Lowering the total debt (in relative or in nominal terms) and paying back are mostly separate things. Outside of crisis situations, many countries can simply roll-over on their debt, offering new ten-year bonds (or whatever) to pay back the ones that expire, effectively “renting” money indefinitely. They can do that because they are expected to keep their ability to pay for a long time in the future. But they do pay back, all the time.

Intuitively, the debtor seems to be the weaker party and to an extent it is but there is much more to debt (sovereign or not) than that. Obviously, creditors also profit from lending. Interestingly, countries sometimes actually borrow money at negative interest rates (taking inflation into account), which underlies how desperate some private actors are to lend money to them in turbulent times.

Also, it's tempting to see a trade surplus as a sign and source of power but it can actually be the opposite, the result from a weak interior demand and an aging population (as in the case of Germany). By an accounting identity, trade surplus is necessarily equal to net capital outflow. Since they do not consume or invest so much at home, Germans sorely need an outlet for all their savings (not necessarily sovereign debt but foreign debt in general) and profit from bubbles elsewhere (say US subprime lending or real estate in Spain before the crisis). 

They can't easily run from that without suffering severe consequences, both parties are caught in this game and the build-up of debt is just as beneficial to the creditors (and encouraged by them) as it is to the debtors.

Incidentally, note that sovereign debt is being paid back constantly. Sovereign debt is not like a credit card, it's issued in the form of securities (bonds) with a fixed term between a few weeks and thirty years. The details vary somewhat but when a bond reaches maturity, it is paid back entirely. 

Outside of crisis situations, many countries can simply roll-over on their debt, offering new ten-year bonds (or whatever) to pay back the ones that expire, effectively “renting” money indefinitely. They can do that because even though they borrow large sums of money, they also have huge resources and are expected to maintain their ability to pay for a long time in the future. But states do pay back their debt, all the time.

So lowering the total debt (in relative or in nominal terms) and paying back are mostly separate things. Individual lenders are not buying a vague promise that debt would go down some time in the future, they are buying a debt instrument with specific properties and predefined payment dates that most states honor most of the time.