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$$$, skills, any one of a number of reasons. TVAL often build a static for their first WW1 reproductions, it helps work out techniques, etc. If this guy hadn't built an aircraft before, which it sounds like, he likely wouldn't have the skills at the beginning of the build.If you're going to take that long, why not make a flyer?
A company called Gate Guardians in the UK do.Why don't they make 1/1 scale plastic kits? For less then $1,000 each anyone could glue together a full size aircraft lawn ornament.