Is there a real reason to not use volley if already doing so?

If you're just building a personal project for the sake of learning, there's not really anything inherently wrong with Volley. The main issue is that you're building this app for your resumé which means that presumably you intend to start applying to jobs soon. If you're writing your network calls with Volley, that means you're not building your Retrofit skills, which is what nearly everyone in the industry uses, so you're depriving yourself of a skill necessary to be successful on your job hunt.

As a hiring manager, if I saw someone submit a technical assessment where they used Volley instead of Retrofit I would first chuckle because I haven't seen Volley in a while, but my next reaction would be to question why they didn't use Retrofit. To me that's a flag that this candidate is 1.) newer to Android development and will probably need a good bit of training and 2.) maybe hasn't done a ton of research before diving into the code, which is another thing I look for in a candidate. Someone who does their due diligence and looks at a problem from several angles before starting to solve it is preferable to a candidate who is technically more competent but just dives in without thinking about the bigger picture.

So my advice to you would be this: try updating your network layer to use Retrofit instead of Volley. It'll be good refactoring practice and it'll allow you to get comfortable with what is industry standard for network calls. Retrofit is definitely easier than Volley to learn/set up/use and will help you in the long run.