To be fair, there were debuggers pre-1.0, but the changes in the language syntax and compiler broke them. That one was just the first one to work with the new architecture that was released on the second half of last year (and since the language is now stable, we can expect it to stay functional and improve over time). There is also another debugger being made with a completely different strategy (embedding the debugger within the compiled code instead of interpreting it):
A Julia debugger was introduced recently [1] but its in a very early stage.
[1] https://julialang.org/blog/2019/03/debuggers