Unfortunately I don't have a direct answer for you on this. However, what does jump out at me from your description is that you describe a utopia environment where developers are guided on a path to their future, own their code, and are recognized for their achievements. Yet, in the next paragraph you state that one of the reasons they state for leaving is "stress of my workplace".
I don't know you, the company, or how you manage, but could the attention you are placing on "career development" and recognition of accomplishments be causing added stress or unwanted attention in the workplace? Maybe they want to come to work, do their job, and go home without this feeling that they are being forced into a specific career path or having to meet certain career development goals.
Anyway, just a thought. It was something that stood out from your description. On the other hand, unfortunately without being able offer competitive pay or technology, many developers may just use your company as a stepping stone. You could try talking to upper management or HR and throw the burden on them. It costs a company a lot more to continuously hire rather than just paying a competitive salary to begin with. Show management how competing more on salary could save on hiring costs.
I don't know you, the company, or how you manage, but could the attention you are placing on "career development" and recognition of accomplishments be causing added stress or unwanted attention in the workplace? Maybe they want to come to work, do their job, and go home without this feeling that they are being forced into a specific career path or having to meet certain career development goals.
Anyway, just a thought. It was something that stood out from your description. On the other hand, unfortunately without being able offer competitive pay or technology, many developers may just use your company as a stepping stone. You could try talking to upper management or HR and throw the burden on them. It costs a company a lot more to continuously hire rather than just paying a competitive salary to begin with. Show management how competing more on salary could save on hiring costs.