Without knowing who you contacted, I can't speak definitively as to why they didn't write back. However, I can speculate. The first two things I'd propose is that the producers in question don't do F/M, or they don't want you, specifically if they do. F/M isn't exactly a huge seller, in my experience, so it's not like they're going to need dozens of models in the same way that they would to cover the */F categories. If that's the case, they may not be booking at this time. Or, the more obvious reason, is that you're not a model. Are you hot? Ripped? If not, odds are they don't want you.
And regardless of the reasons, making a pest of yourself would immediately take you off "the list" even if they were considering you in the first place. Generally speaking (and this goes for any business venture), you're allowed one follow-up. Beyond that, you've gone from "interested" to "annoyance", especially if you're at the stage where you're E-mailing them on a weekly basis and begging for an answer. (And before you say "I'm not begging", yes you are.)
As a producer, I am not going to work with someone desperate for a "tickle fix", especially not some depressed dude from the TMF who started a thread to complain about his lack of "experience". It wouldn't be hard to put two and two together and realize that you're the guy in my Inbox begging to come to my studio and noping you right into the Junk Mail folder.
I'm not a big name, but I get guys contacting me angling for an "in" once in a while. They want to come "help", but what they really want is to get their hands on the girls I work with. There's absolutely no way I'm risking my reputation by letting some random stranger from the Internet into a shoot, so unless you come knocking with a modeling resume, portfolio, OMP profile page, or something similar to show me you're looking for legit work, I'm going to assume that's what you're up to and your E-mail is going into the circular file. Bluntly, we're not in the business of setting up tickle sessions between our models and randos.
So, my advice to you is to forget about hooking up with a studio and go with what the other people here are telling you instead. Making videos isn't for you right now, if ever.