With respect, this is because you know how Disney works. You know the lay out. You know how FP works (and how to refresh). You know about RD and riding at the end of the night. You know which restaurants need ADRs (and, if I recall, this doesn't apply to you because you bring all your own food). You have a realistic understanding of which rides will have crazy lines if you can't get FP. But if a newbie just plans to walk up to the castle and have lunch with Cinderella, that's going to be a problem, if that person's children have been looking forward to that. If a newbie shows up expecting to ride 7DMT and the mountains before lunch, and doesn't know about the FP system and the length of standby lines, that person is going to be disappointed. Many of us could show up tomorrow and still have a good time, but that's not the case for many newbies.
Story time. I was waiting in standby at HM last fall before my 7DMT FP window, and noticed a large family group (like 10 people) behind me. We started chatting and found out it was the 11-year-old's birthday and they all decided to go to WDW and bought tickets at the gate. I asked what FP they had planned, and the mom said none. I asked why, and she indignantly replied, "because they're too expensive!" I was like, "they're FREE!" So I spent the rest of the time in line on her phone setting up an
MDE account and linking the tickets for all of them (except for a college age son and family friend who had their own MDE accounts and would need to link themselves). Anyway, I hope they were able to set up at least a few FP for the day, as we got to the ride entrance before I could do that. But I explained how it worked. So this big party of 10 was going to wait all day in standby lines simply because they didn't know the basics of FP. Would they have enjoyed themselves? Probably, but not as much as with FP. And if they'd gone at Christmas or Thanksgiving, forget it - standby all day would be a nightmare.