On a logistical level, it's much easier to start a 3-year trial than a 30-year trial. Tracking people for 30 years is more challenging. Giving an experimental d

On a logistical level, it's much easier to start a 3-year trial than a 30-year trial. Tracking people for 30 years is more challenging. Giving an experimental drug to healthy people for 30 years is challenging and ethically more delicate. But perhaps from the view of the scientists, motivating yourself to perform a trial that won't yield results for 30 years is quite an effort.