Because it writes like BASIC and C had an unholy love child--vaguely C-ish in style, but it lacks case-sensitivity and uses stupid stuff like BEGIN and END.
Note that I've never done straight-up Ada, just the derivative VHDL.
I'm always skeptical of this argument; every programmer has a favorite syntax -- some prefer C-like, some prefer Pythonic, some prefer Lispish, etc. In most cases, it's not the syntax they first learned, but it's the syntax in which they do the majority of their work. This suggests that familiarity is the basis of syntax preferences, which supports the "you'd like it if you gave it a chance" school of thought.
I assume you mean that syntax is less important than other language features, and I mostly agree. However, while there are of course many variations of syntax on the same basic set of features, some variations are better than others. It may be difficult to say whether Python, Ruby, or C syntax is best, but that doesn't mean that some aren't better than others.
For instance, terse languages, as long as they remain understandable, generally seem better. Whether to use braces or indentation may be a matter of preference, but few would argue that a COBOL-like syntax is preferable.
Note that I've never done straight-up Ada, just the derivative VHDL.