1. Lack of memory safety is a big problem particularly because it's a common cause of dangerous vulnerabilities, but spatial safety is more important than temporal safety for that reason, and Zig does offer spatial safety.

2. Other important issues of concern when it comes to security/correctness are language complexity and compilation speed. A complicated language with lots of implicitness can obscure bugs and make reviews slower. Slow compilation reduces the iteration speed and harms testing. Zig focuses on these two. The language is simple, with no implicitness - overloading of any kind is not allowed and neither are any kind of hidden calls. Even if security were the only concern, it's not clear at all how much complexity and compilation speed should be sacrificed for temporal safety. Remember that it's easy to classify bugs by technical causes, but more diffuse aspects, like testing and review, are also very important, and Zig tries to find a good balance.

3. Nevertheless, the language is still very expressive [1]. In any language, you want the algorithm to be clear and with neither extraneous nor important hidden details for that domain. I think Zig gets that about right for low-level programming (and C++ doesn't).

For me, the #1 problem with C is lack of safety and the #2 problem is lack of expressivity. With C++, the main problem for me is language complexity and implicitness, with slow compilation and lack of safety tied for number 2. So Zig is as expressive as C++. but not only safer, but also much simpler, and compiles faster (and improving compilation speed further is an important goal).

[1]: I say that two languages are equally expressive if, over all algorithms, idiomatic implementations in both languages (that are roughly equally clear) differ in length by no more than a linear relation with a small constant.