Why do Roadie Commuters seem to have to take the added risks of always riding on the road despite there being a perfectly good and lovely to ride on bike path/MUP next to them?

I've noticed this a lot recently. There are two MUP's which are really fine to ride on on my route in to work both of which are right next to busy roads. Both MUP's can be used at speed as during rushhour as other times there is hardly anyone on them.

The stretch of road next to one is horrendous and fast and you have only a tiny amount of space at the side of the road to ride in, this space has around 20 manhole covers along it. Taking the lane is impossible due to the speed of the traffic and I've not seen even the most courageous VC roadie manage it yet in 3 years. I use that road very rarely and only if the traffic is not too heavy and I'm very late for work, it saves you about 5 minutes. I see roadie commuters and only roadie commuters use it daily why take the risk? By leaving 5 minutes earlier you can have a stress free and lovely to look at ride on the MUP?

A couple of months ago I was on another MUP which runs next to the State Highway, it was gusting up to gale forces and the wind was moving me and I'm not light with around 10kgs of shopping on my back, around the bike path. Up ahead I spot a roadie commuter on the side of the highway being pushed into the traffic by the wind! I see her regularly, she knows about the MUP because it known by everyone and is well signposted. There is nowhere else to go, both the MUP and the highway go to the same place.

Why do Roadie Commuters have to use the road all the time? It defies logic and common sense.