You can't just expect to use this conversion and always be able to make it work.
Company you worked for might have proprietary tech, patents/IP, massive clients you'll never be able to get, etc and thus can pay you more.
If I work for Google as a search engineer making $200k it doesn't mean I can leave and then suddenly earn $800k selling search consultancy services to DuckDuckGo and AskJeeves.
If I'm an accountant at Deloitte making $120k auditing Fortune 10 companies it doesn't mean I can leave and make $480k revenue auditing sandwich shops and I probably won't be able to take any of my previous clients.
Company you worked for might have proprietary tech, patents/IP, massive clients you'll never be able to get, etc and thus can pay you more.
If I work for Google as a search engineer making $200k it doesn't mean I can leave and then suddenly earn $800k selling search consultancy services to DuckDuckGo and AskJeeves.
If I'm an accountant at Deloitte making $120k auditing Fortune 10 companies it doesn't mean I can leave and make $480k revenue auditing sandwich shops and I probably won't be able to take any of my previous clients.