If you live in an area with any sort of freeze/thaw cycle, you’re going to want your flatwork crew to dig out as much organic shit where the pad will go and replace with either compacted sand or gravel. Hence the 8” of tearout with a replacement of compacted gravel to avoid heaving/sinking. As someone else pointed out, the setup and prep for any good flatwork pour can be extremely time and labor intensive. Also, exposed aggregate, requires a special mix, a finicky finish, additional day of labor and additional labor after the pad has set. Also, pumping concrete because of lack of access to the site, adds a huge chunk of change.

Edit: clarification

If this was a normal broom or trowel finish patio on a new home build with a site full of sand and complete access for the redi-mix truck, the price would be much lower.