Even from the west coast it's a 6 hr flight. Combined with time difference, it often means 2 days on travelling alone. Even worse for people in mid west or near west coast, which is the majority of where the population is [0]. For most people I know, Hawaii is a trip once every few years, and definitely not twice a year.
This is a week vacation though, not a weekend. I agree it doesn't work for a weekend, but if you take a full week off things look much better. If you really do want to go to that exact place in Hawaii for one week a year every year for the rest of your life a timeshare is a great deal (assuming the fees are as stated, sometimes what looks like $100/month turns out to be $2000/month) - but I don't know many people who vacation like that. I do plan to go back to Hawaii, but I also have vacation plans for Boston, Florida, California, Spain... Even the people I know who do vacation like that don't do it for life (I make regular trips to visit my in-laws, but they are thinking about moving states so I may have already taken my last visit to their current home)
In the end, the best case a timeshare does save money. However for most people the restrictions mean you are never in the best case and often you are in the worst case and lose money.
[0] http://dhmontgomery.com/2018/02/population-latitude/