There can be parser considerations:

    a < b

can be greedily interpreted as a comparison, despite the next character being a >

    a [ b

can be greedily interpreted as accessing a field in a map, despite the next character being a ]

It may be easier to branch in one of those cases instead of the other.

Not at all familiar with the potential issues (if any) in go, but this is from experience in writing a few languages.