Not an immunology expert, but the focus on antibody titers seems to reek of corporate conflict of interest. It's pretty well understood that antibodies will break down and mostly fall to undetectable levels after a few months of an infection (in most cases, and in individuals who actually produce antibodies, not everyone will such as immune-compromised people) , but there's a
huge financial incentive for vaccine producers to focus on these studies because it paints the picture that people need continuous boosters for protection. That being said, it's harder to detect other forms of immunity such as memory T and B cells, so it's not like the studies are completely disingenuous, it's just easier to do the studies that way.
At this point in the pandemic, I think full immunity shouldn't be the goal for most individuals. COVID and it's variants are never going away, so unless you are high risk, live with someone who is high risk, or travel a lot, the first round of vaccinations should be good enough to prevent serious illness in most individuals for a long time, at least until a variant that changes the spike protein enough comes around. At which point, to my understanding, the efficacy of most vaccines will drop significantly below natural infection, as most target specific protein structures on the virus capsid (in this case, the "spike protein").