I've submitted literally 2 dozen proposals. I even attended a talk for submitting a winning proposal and implemented the strategies. I have a (in my opinion) well-build portfolio site.
However, not one of my proposals has been accepted. I've been applying high and low, too - diffeent types of jobs (sketchy/well-written), different pay (below client's budget/above/within).
I am not sure about your field of work but from what I know, a lot of it depends on your proposal. So make sure to write a detailed proposal every time to apply for a job which explains how you will attempt the given job.
All the best