Stamps or sets?

Since I am missing only the 3 big sets of Israel tabs(7-9, J1-5, 10-14 vertical gutters), each of which goes for around $5000, I figure I never will be able to finish my tab collection. It will be nearly impossible to have enough money available for my stamp collection to buy these stamps. I guess I could stop buying stamps for a year or two and save my money for these, but what is the fun in that? I have been adding other items to my collection over the years, and can't see going 2 years without a new addition. Wouldn't it be nice if the stamps were sold individually? That way, I could pick up a 7 here, a J2 there, and eventually get them all? Unfortunately, rarely (if ever) are the stamps sold individually. When I see them offered individually, I have shied away from these for now, since they are offered so rarely (and I have never seen them offered this way from dealers in price lists or at shows) that I am afraid I am never going to be able to find the ones I need offered individually. I know that US stamps are routinely offered individually, rather than only in complete sets. Why are Israel stamps only sold in complete sets?