A lot of things that basically boil down to budget, optimization and space available. If you have a drug that you believe you can show a strong effect with the effect group at ~15 people, maybe you run the trial with 40 (15 e.g., 15 control, plus wiggle room for drop-outs over the 18-month course and extra certainty).

Check the last few paragraphs--"The authors thank Shayna Greenberg, Dev Darshan Khalsa, and Anya Rosensteel for help in recruitment, data management, and study coordination; John Williams, University of California, Los Angeles, Nuclear Medicine Clinic, for performing the PET scans; and Vladimir Kepe, Cleveland Clinic, for developing the FDDNP-PET analysis procedures for proteinopathies in patients with neurodegenerative diseases." Add all that to the effort involved in the actual chemical extraction of the bioavailable curcumin analogue and it just doesn't make sense to add any more people than you need.

For the recruitment, data management, and study coordination piece, sounds like a great area to optimize with software. I'm sure big pharma will also happily shell out for something to help them manage their own clinical trials. Academia PIs can then get the same stuff at a lower rate.

Edit: Heck, you can even lease top grade medical space in all major metro areas and offer it as part of the package in a WeWork style arrangement. I'm sure they are tons of nuances to rolling something like this out, but it sounds like it can cut costs substantially.

If they're marketing their own drug (as implied by other comments - I don't know), you might also ask what stops them from running the studio on a 100 groups of 40 patients, and picking the "best" for publication... (other than ethics, obviously)...

Cheaper to run it on 100 and select the best 40 to report in your study.

As others have pointed out. Its about money. If the compound is expected to be very profitable, then it make sense to invest a lot money to do a large scale study. On the other hand, if it is a natural compound that you can't really patent, the profitability will be much lower. It doesn't make sense for a commercial entity to do a large scale study. If the compound is important enough, a government entity will sometimes invest the money to study it.

Money.

Funding