HCL is also oodles more complex than TOML since it has expression evaluation, whereas TOML is just a static format. It really depends on your use case and I think there's a lot of cases where TOML makes a lot more sense than HCL (e.g. metadata formats).
HCL also has expression evaluation however: TOML parsing is guaranteed linear over the size of the file, but HCL isn't necessarily because you can trivially do things like dynamically create a n*n-sized list from n-sized input list, which may be an undesirable property!
