There are any number of reasons why promising lines of research get stuck. Simple abandonment is a surprisingly common one; people outside the scientific community have little appreciation of the degree to which the floor of the forest is littered with valuable raw materials, just waiting for someone to spend the effort to forge them into useful goods. Many researchers have little interest in implementation, or fail to convince funding sources to continue their initial exploration, or the people involved move on, or the tools are hard to use and no-one else wants to make the effort to replicate the discoveries. It is sometimes amazing that anything is accomplished, watching the way in which most academic labs organize themselves.
Another common problem is the lack of suitable tools to manipulate a mechanism of interest, related to disease or aging. Once researchers find a mechanism, and have the means to probe its operation, the next step is to build ways to influence it. Some of the most common traditional tools are genetically engineered animal lineages, in which genes of interest are inserted or removed in the germline, gene therapies that increase or decrease protein levels in cells and adult animals, and small molecules that can increase or decrease protein levels, or interfere in or enhance protein interactions. Of those, only small molecules have traditionally resulted in clear path to clinical application, though gene therapies are starting to become more practical for those purposes.
What happens when researchers have an interesting mechanism, but don't have a small molecule that can manipulate that interesting mechanism? Well, they are stuck when it comes to moving closer to the clinic, unless they can raise a fairly sizable amount of funding for screening, as well as produce a sufficiently cheap screening methodology to allow a very large number of compounds from the standard libraries to be tested. The cost of a comprehensive screening exercise to find candidate small molecule drugs can be a few million dollars, which is why there are a sizable number of companies working on ways to reduce that cost and raise the odds of success. Expending these sizable resources offers no guarantee of finding a viable compound, or even a viable starting point. That is why many projects just stop right there, and remain halted until the slow grind of grant-writing and incremental discovery leads to a potential candidate compound in some other way.
In recent years, the new ability to cultivate arbitrary bacterial species from soil, rather than the tiny minority that has traditionally been the case, has unlocked the door for compound discovery relating to destruction of problem molecules. Every molecule in the human body can be consumed and broken down by at least one species of soil bacteria. Finding the tools that bacteria use for that purpose is low-cost and reliable in comparison to old-style screening from compound libraries: just grab a soil sample, separate the bacteria, drop in the protein that needs destruction, and see which of the bacteria thrive on that diet. A number of research groups have produced proof of principle results with modest budgets.
While that works just fine for targets such as the 7-ketocholesterol associated with atherosclerosis, as well as glucosepane cross-links, both of which are implicated in the aging process, and that we'd be far better off without, the approach doesn't work when the objective is to alter rather than destroy aspects of cellular metabolism. For example, it would be very useful to have drugs that interfere in the operation of alternative lengthening of telomeres (ALT), a mechanism that is only active in cancer cells. All cancers must lengthen their telomeres constantly in order to maintain rampant growth. If both ALT and telomerase-based telomere lengthening could be suppressed, then cancers would wither.
Work on finding ways to manipulate ALT is essentially stuck on the point that someone needs to spend a few million dollars in order to buy a chance at finding a candidate small molecule drug. No-one really wants to take that wager, and would much rather wait on incremental progress in the field to turn up a possible path forward. Perhaps that will happen in a year, perhaps not for twenty years, no-one can tell. It seems to me that for those areas of research blocked in this way, and where success would be very valuable, then paying for the screening would be a sensible act of high net worth philanthropy. For that to take place, however, it would require either a good understanding of the field on the part of more wealthy individuals, or a good packaging of the ideas involved on the part of a non-profit entity.