We life in an age of change and rapid scientific innovation in medicine. That in and of itself might be enough to explain why historical actuarial predictions of longevity have been low in comparison to the actual outcome: extrapolation of existing trends tends to do poorly in the face of consistently unpredictable innovation.
Nonetheless, a large industry is focused on getting these numbers right, or as close to right as is possible, as vast sums are promised to older folk, either as political entitlements or honestly obligated as a result of insurance contracts. Betting against increasing longevity seems like a fool's game, but nonetheless there is a lot of money to be made in that business - many large entities want to be protected from what is known as longevity risk, the risk that life spans will rise faster than expected and thus financial obligations will spiral out of control. Large entities are willing to pay for that insurance service, and taking on risk for a percentage is very much the core business of finance.
In theory the people taking on that risk for a percentage know what they are doing, and they are the ones funding efforts to understand the risk - which in this case means models for future increases in human longevity due to advances in medicine and biotechnology. In practice? The risk gets sliced and diced and parceled out among the players in finance, that much is true. But I'm sure we all see the present results of that undertaking in other large industries, such as housing: when there is enough money involved the business becomes one of lies and politics, the fine art of pocketing profits, taking on unknown risks for short term gain, steering government policies, and raiding the public treasury to cover losses when it all goes south. When buying politicians and policy is a reasonable cost judged against the cost of contracts, buying politicians and policy becomes a part of doing business - and very lucrative, since it allows risk-bearers to try for the upside with the expectation that they will be bailed out if it fails.
Thus a web of perverse incentives grows, benefiting the connected few at the expense of the many. In the course of all of this, there is an increasing pressure (and ability) to obscure or water down unfavorable data, especially when the interests of profiteers and government appointees coincide. Again, we've all seen this come to pass numerous times in recent years and prior decades. It is the way of the world, and just as much so when it comes to the future of human longevity:
In 1981, the United Kingdom (UK) Office for National Statistics estimated that male life expectancy at birth would rise to 74 by 2031. It hit that age in 1994. In 2002, the 2031 estimate was 81, but we are now expected to pass that in 2019. This systematic underestimation of official life expectancy increases occurs around the world. It is not an accident. It is deliberate. Politicians put pressure on official agencies to do this, so that the full cost of longevity increases does not fall on them or the current generation of voters. The reason is clear: If more accurate and hence higher projection of life expectancy were produced today, then social security contributions would have to rise now rather than later - and this would be politically very unpopular.
The powers that be and their predecessors have accomplished what powers that be always manage in the end: to set up a system of wealth transfers and entitlements that is both unsustainable and stands in opposition to true progress. Thus the modern spectacle of people trying to argue that increases in human longevity are a bad thing! The collapse will come, the promises that cannot be kept will be broken, that much is certain - although it is true that modern innovations in fiat currencies have allowed the game to go on for a good deal longer and become a good deal more destructive than was usually the case in the past. But eventually they will run out of other people's money to loot. Along the way to that end those who are trying to prop up the house of cards will undoubtedly build a great deal more in the ways of lies, waste, and other unpleasantness.