What skills or competencies do they lack?
To start out the definition of "marketing" has been totally been siewed for the last 10 years. Most young people today think it means advertising online, SEO, and the remainder think it means graphic design and flyers. Just like marketing could mean a lot of things digital marketing can also mean a lot of things. Most newbies in digital marketing are going to be dealing with compiling Analytics, designing ads that someone else gave them specific instructions to create, I'm physically placing, uploading, and deleting ads on various platforms. You can imagine how tedious this all can be, that the Newbie probably doesn't understand the ultimate objectives of the campaign, that the work is very repetitive, and that a lot of mistakes can be made which are there have to be corrected at a large cost or at least managed. Most of these newbies do not know the most fundamental aspects of marketing as a practice: the P's, awareness, emotional drivers, etc. Without that how can they really make the right decisions or understand what they're doing in context? This is a roundabout way of saying most of these entry-level people lack fundamental and foundational knowledge of marketing as a practice, so managers are frustrated because the people they hired really don't understand what they're doing outside of what they're doing
I have hired various levels of marketers and also worked at a startup that sold a SaaS recruiting platform which gave me insight into how the leading recruiters and hiring managers think.
I my experience entry-level hires in general need to energy, intelligence, focus, and a willingness to learn. Character and temperament is more important than specific skills. They may still be figuring out what they want to do with their lives so a marketing background is a nice to have.
From working at a recruiting software startup, I can tell you that all hiring managers are busy and might not have the ideal amount of support during the hiring process. They want the hire to be a good candidate but mostly to make it easy on them.
Experience, experience and experience.
I hire junior marketers and I'd always favour practical experience with demonstrable real-world results over an academic qualification.
So, if I was looking for an entry level marketing job, I'd set up my own micro business, apply what I had learned in college and create a case study.
If you are as good as you think you are, you might not need the job after all ;-)
I hope this helps.
Happy to advise on a call.