It all comes back to comparing bonds with their alternatives. Here is a sample of government bonds I grabbed. Have a look at the yield column.
I can get 2.9% by sticking it a savings account at my bank. And if you want it "locked away", you can use term deposits. That's your benchmark. The sorts of returns I'm seeing on government bonds isn't comparing with that, in most cases.
The other downside of bonds in general, is that their capital isn't secure. Their value fluctuates. Unlike a bank deposit, they're a risk product. If my money is at risk, I want a much higher return.
Yes to shares. You can park your money in a cheap, broad-based index fund and get around 11%. But be prepared to leave it there for 7+ years, say, as the market can fluctuate quite a lot.