The table on page 129 of the DMG lists the costs to craft an item.
Taking as an example a Common magic items, such as a level 1 spell scroll, the cost is listed as 100 gp. The crafter can only make 25 gp worth of progress per day, so this takes 4 days worth of effort, at 8 hours per day. The crafter must use a spell slot to cast the spell once on each of those days.
Meanwhile, the guidelines on page 139 for the costs of magic items states that a common magic item is worth 50-100gp with consumables, such as a spell scroll, costing half. So a first level spell scroll "should" cost at most 50 gp.
Looking at the tables for other rarities of items, again the creation cost is listed as the maximum of the suggested values for items of that rarity, and that doesn't even take into account the value of the crafter's time to work for many, many days to craft it.
Am I missing something here? Can someone explain how this makes sense?
(Obviously, this assumes a campaign where at least common magic items are available for purchase)
I understand that the prices listed in the DMG are suggested starting points only, but why are the suggested starting points for item values inconsistent with the suggested starting points for item creation?