The government, in offering this choice, is taking a calculated risk, and the pensioner likewise. You're taking a gamble on living long enough to get the enhanced pension. If everyone who chose to defer the pension had the right to claim the money for their estate if they died, the system would collapse - it relies on those who die early subsidising the pensions of the long-lived.
You don't have to do it. When we were offered the choice, we thought, "Do we know we'll live long enough to benefit? No. Do we trust future governments to honour the agreement? No. Do we want to end up paying more tax (because the money is coming in a lump or at a higher rate, rather than being spread thinly across all the years)? No. We decided to take what was offered as soon as it was available.
In fact, my husband - despite being a fit, well nourished and otherwise healthy man for his age - died of prostate cancer at 68 - so it turned out to be the right decision for us, as the deferred money would have been lost to us..