UCT fits free market theory, including market flexibility (if needs change or the first idea fails, consumers can change their spending much more quickly than donors can change their programs), and promotes democracy and empowering individuals. It also avoids common problems such as donors' bad decisions and their unanticipated consequences, corruption among those controlling distribution of the goods, and perversion of local markets.
As one example, according to a report in Foreign Affairs, the West's focus on AIDS, malaria, and TB, and their relatively enormous market power, took local medical resources away from more standard health care needs such as child birth, and might have resulted in more sickness and deaths than it prevented (IIRC the details of the article from several years go).
In brief, unless the nation is in crisis, send fishing poles, not fish.