I know what "microlights" look like.
Your remark regarding open cockpits suggested otherwise. Might have been a stab at humour, of course.
I also can't believe that the closed cockpit tricycle gear ones cannot carry a 7kg raft
Nobody said they can't - the issue is solely a legal one. Most of these craft are, or could technically be, certified as LSA's in the USA, without any modification, but with 20% more MTOW, iow a hundred kgs more payload.
Far more likely, it is against the "community culture" to spend money.
Surely microlighting is about pragmatism, and about limited budgets. It takes a rich person today to go blundering about the skies and paying as much as it takes, regardless.
Myself am not going to spend a single penny on a raft until I see clear proof that it has at least some chance of saving my life if/when going down into Neptunus' welcoming waves.