Well, unless I'm some kind of oddball (I am, but I don't think this is one of my peculiarities), then it's very bad advice. For me, no table of contents = no sale. At least, if it's non-fiction. Very often I won't even bother trying something on kindle unlimited if there's no table of contents.
1. Besides the reasons in my first post, no toc screams amateur. There is a direct correlation I've found between the quality of the writing and editing and the presence or absence of a toc.
2. Again, sticking with non-fiction - you aren't always interested in the whole book. You might just be interested in what would be in chapters 4 and 6, if you could find the #$$!!##s !
3. Related to point 1, when I see no toc, I don't think "ah, economising on preamble so that they can show me ten pages of their excellent writing!" - I think "disorganised brain, probably no structure, and I'm gonna have to wade through loads of waffle hoping I don't tune out before I get to the good bits, if there are any"
Anyway, the "look inside" feature is not restricted to the first pages in strict sequential rider. I've sampled many books with this feature that skip the opening pages and go straight to chapter 1 (in these cases, I give them a chance if it's kindle unlimited, and download to see if there's a toc. If there's a toc, I keep reading. If not, I give it back. Non-fiction books aren't worth reading, even for free, if I don't know what I'm going to invest the next several hours or days of my life reading).
ps - thanks though for explaining why authors do that!