What is the difference between tearing out the third row to build a platform level to the second row and just folding the third row that is already level with the second row? Only reason I could see is to build storage into the platform that isn't there with the seats folded down.
I understand people that don't need the seating of a third row, likely most people. I think this is marketed for people that do need the flexability of that extra seating. Bigger families or families that transport other kids/relatives/sports teams etc.
If you want an SUV without a third row toyota makes a 4runner that's still a true body on frame SUV unlike most other manufacturers. 4runner is probably better in all off road conditions due to its size.
If you like driving a big SUV but don't need the seating you have to make compromises. Manufacturers can't market vehicles to individual wants/needs. The biggest need for large SUV is more seating capacity and that's where Toyota aims the Sequoia.
Storage and less weight. May not be much storage, but enough for recovery gear, tools, and non-perishable foods. The gear I pack there likely weigh the same as the seats, so "free" weight and space so to speak.
I give Toyota props for being brave; as you said, most buyers want space / seating over offroad capability. Toyota WILL lose many buyers over that 3rd row. Good news for this community.
Most of my overland travels are not technical; I enjoy extended stays in the BC backcountry, so space matters. Toyota surprised me, this is literally the only time in history I've seen an IRS SUV go the opposite. I grew up in the 90s drooling over big Ford GM SUVs I couldn't afford, so this is nostalgic for me, including the "can't afford it" part ?