Any particular reason only the top 4 seeds at Slams are guaranteed their seeding? - eviltoast

Each of the top 4 seeds gets their own quarter, with all things going to seeding would put 1-4 and 2-3 as the semifinals which all makes sense. But the Slams seed down to the third round (32), but don’t maintain this pattern, at least not completely. For example, in the US Open Men’s Singles this year, the first couple seed matchups in the third round are 1-26 (not 1-32), 16-24 (not 16-17), and 12-19 (not 9-24). They still maintain each seed having their own slice below the third round, just curious as to why they randomly distribute 5 through 32 through these slices of the draw.