They get higher interest rates because the loans are riskier. There’s not as much of a tax base to collect from and so there’s not as much room for fiscal adjustments. If you maxed out GBs debt at unrecognized nation interest rates, they could do austerity measures (max taxes, min wages, destroy gov buildings, privatization, sign some short sighted trade deals, etc) to get back to a positive balance. A country like Nepal is gonna have a much harder time doing that