Most Rust code is quite portable, targeting ARM, x86, MIPS, PPC, WASM, Sparc, s390x, riscv, ... That means, that for many snippets of inline assembly, you might encounter ~8 of them, one for each architecture, all using different syntaxes.
Intel syntax is quite similar to that of other popular architectures `op dst, args...`.
Adding another second syntax for x86 just doesn't add that much value IMO, and adds quite a bit of cost: now everybody dealing with x86 assembly needs to learn 2 syntaxes... and everybody dealing with portable code now needs to be at least able to read 2 syntaxes for x86... Without talking about the cost of implementing a second syntax in the compiler, etc.
If you prefer AT&T, you can always write a proc macro that translates it to Intel, and use that in your projects.
If I ever need to deal with such code, I'd just expand the macro to read the actual Intel syntax, modify that, and either fork the project, or submit a patch with a fix using Intel syntax.