They are cheaper. For now, if your plan is to stay consistently in non-studios/lockoffs during off peak times (mid-Jan-early Sept, minus holidays), are flexible with your travel dates (plus or minus x days), it's more cost effective to get SSR points (on a $/pt/year basis). I think a lot of people who do this successfully are very relaxed about where they stay. If they end up at SSR, it's not the end of the world, but there are no plans to stay there regularly.
If an owner can consistently find success staying elsewhere at 7 months, points are points are points at that point, and SSR is certainly a sensible way to go. Others see too much risk in the nature of long term commitment to a timeshare to risk the system changing and being able to do this 20 years down the line.
Through my own personal first bookings with
DVC, I'm quickly learning that I do not share the patience nor flexibility to go the SSR route, and that in the long term, I can see becoming one of those owners who would be better served getting where they would be happy staying. But who knows? How I travel today will likely change in 5, 10, 15 years.