People leave private practice for the public sector all the time. Fewer hours, good benefits, predictable pay increases, a pension (possibly), no office rent, no secretary/paralegal to pay, no bar dues, no need to carry malpractice insurance, and no Westlaw/Lexis subscription are just a few of the reasons.
Depending on the particular government agency the salary may not be too bad, either. At most DA/PD offices in my area starting pay is $65-70K, reaching about $100k within five or six years.
Minus all the overhead I just mentioned, can the average solo practitioner really expect to make much more?