I live in Brazil, so if the government defaults, every other investment I could have made here would also crash, and the local economy with them. It's not called the "risk-free" interest rate for nothing: it's the lowest risk investment one can get within Brazil. Corporate bonds, for instance, will have a higher return, due to their higher risk.

As for inflation, when it increases the SELIC/CDI rates tend to rise with it too. And if you're afraid of that (it hasn't been long since we had a hyperinflation, so a lot of people still are), another government bond (NTN-B) has a return of inflation (measured by the IPCA index) plus a pre-fixed component (currently around 6%). Due to its pre-fixed component, it has some interest rate risk (if the interest rate rises, its present value drops, and vice-versa), but that's not a problem if you intend to keep it to term.

And, actually, the high interest rate is set by the government, as a way to control the inflation, so it's not as linked to the risk of default as one might think. The government could decide to lower the interest rate (and it has: a few years ago, it was set lower, but that led to the currently higher inflation, so the government increased it again to contain the inflation).

That's not true for domestic currency bonds. There's no chance of default as a sovereign can always print more of it's own currency. Sovereign yields are driven by inflation expectations and what investors need to earn on excess of that.

This is all true - and if you look at the UK gilt price/yield over the last six months it demonstrates this aptly - yields started to increase in June as everyone tried to sell their gilts. As you say, the yield only happens if the government pays the nominal at the expiry - and if yields are high it's because the market lacks confidence, and people are selling for less than nominal.

long live the carry trade