The recruiter won't care much about why you want to leave a job. Their primary focus is to get you into a new job in order to collect a fee from the employer. The recruiter will ask you some basic screener questions while very likely not understanding what it is they are asking. If this is an internal recruiter the questions likely came from the hiring manager. If it is a staffing agency, you're lucky if the recruiter even has a direct relationship with the company. More likely they're one of a dozen+ companies trying to find a warm body for to put in front of the company. I often receive several LinkedIn messages for the same job in my local area from various staffing firms.

One thing you should do is take a look at your list of negatives and turn them into positives that you have to offer a new employer. For instance, the item about many senior engineers joining and leaving can be turned into, "I have been exposed to a broad range of coding styles and architectures from working with many codebases built by knowledgable developers. Supporting and maintaining them in a production environment has allowed me to see what works well, what doesn't, and to better my own style." Be prepared to give one or two examples of how you were influenced by the good and the bad. If I were interviewing you, I would ask for them.

Regarding your first two bullet points, you probably shouldn't be interviewing for junior positions with four years of experience. Make sure that you're interviewing for mid-level positions. It's rare to be asked why you want to leave your current position. If it happens just say that your company is in a hiring freeze and that you're doing the work of a mid level programmer but are unable to be promoted and that you need the extra income to purchase a house.