20th Century Type Set vs Modern Type Set

Why did PCGS include commemorative and bullion in the Modern Type set and exclude them from the 20th Century type set? It'd be much easier for my children to complete a type set (1950-date) w/o silver, gold and platinum bullion. If PCGSs mission is to help grow the collector base (our children), they should offer registry sets children can complete.
WANTED: Cincinnati Reds TEAM Cards
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As for PCGS's mission I think that is to make money, the ANA has a mission of devoping new collectors I think.
My 20th Century Gold Major Design Type Set ---started : 11/17/1997 ---- completed : 1/21/2004
I do remember a time when I looked at a 20th century type coin folder and laughed when I saw the slots in the back page for gold coins. I thought there was no way that I'd ever own all of those--a Type I and Type III gold $1 (but no spot for a type II), and one each of Indian and Liberty $2.5, $5, and $10, plus Liberty and Saint Gaudens $20s. About a month ago, I finished that set. I don't have the folder any more, and most of the coins are in PCGS and NGC holders, but that aside, in essence, I filled that back page completely before any of the others.