Physics reasons: This blog post by Mike B Hopkins, following up this previous one, suggests that the Focus Fusion results are consistent with other experiments and calculations and known scaling-laws, and that the fusion is coming from ion acceleration rather than high temperatures, and that (related to this) this is not an approach that can possibly produce net power.
(I don't know plasma physics, I cannot vouch for this.)
Aneutronic fusion is a real thing, but requires 10X higher temperature than D-T fusion (according to wikipedia).
1. The founder Eric Lerner is one of only two people officially affiliated with the company who has any professional plasma physics experience. Not only working there, but even on the board of advisors! (The other one is their "consultant" John Thompson, whose PhD training was not in plasma physics, but apparently he did applied plasma physics at companies afterwards.)
This suggests that either (A) Dr Lerner cannot convince any plasma physicists that this project is worthwhile, and/or (B) He is too cocky to want other professional plasma physicists to be involved, and/or (C) Plasma physicists do not want to work with him for whatever reason.
2. Eric Lerner has crazy ideas about astrophysics (he thinks the Big Bang theory is wrong, that the universe is not expanding, etc.). OK, no big deal. A lot of people have crazy ideas about something or other. It doesn't automatically mean they are incompetent in their areas of core expertise. But, the fact that he is promoting his personal crazy astrophysics ideas on the fusion energy company website, rather than on a separate personal website, is weird and disturbingly unprofessional.
Since the success of an experiment (to say nothing of a business) depends not only on sound physics but also on people-skills and managerial competence, I think these are legitimate reasons to guess that the experiment will fail.