At first this was a feature I was excited for. After using it, I've changed my mind about it. Constructor property promotion was added so that you could pass an argument to a class constructor, and it would get auto assigned to a property, without you having to do $this->That = $That in your constructors over and over.
The main point of attributes is to add metadata to code that is easily parseable and can think for itself when you ask for it. Up to now most devs were probably doing this using the PHP docblock thing - those double star multi-line comments. We'd fill them with @tags and then parse that data with Reflection and probably some regular expressions to make any sense of the blob of text.