There are a ton of reasons for which someone might not respond to unsolicited quotes, and I'll do my best to explain. Without seeing the specific email you sent, it's all guesswork though.
1) Freelancers are generally busy right now, and it's hard to keep up with potential customers that may or may not work out when you're already bouncing time between two or three active, paying customers that are a known-good quantity. This leads into,
2) Lots of freelancers aren't set up to be agencies. The main difference between a freelancer and an agency is that an agency has someone following up on potential work while there is someone different actually doing the work. For non-agencies, this means that every customer I'm ironing out terms with or trying to get a sale from is time away from paying customers and real money in lieu of potential money. Obviously, it costs a lot more to work with an agency because now you are paying for at least two people, and also paying for the time that gets wasted, but it is generally the more reliable way to go if you can afford it.
3) If you mention a specific toolset (e.g., Rails, Django) in your message, it might be that the folks you're sending to either aren't familiar with that toolset, or they don't think it's appropriate for the task, or in some cases, I've seen people simply avoid working with customers that asked for a specific toolset. The logic there is that people who ask for things like Rails, but that aren't competent to build the thing themselves, often don't know what they're asking for and that could be in indicator of a difficult client. Obviously this may not be the case, you may simply have another codebase that it needs to work with, or y'know, any of a hundred different reasons that you actually need something written in Rails, but that is the perception I've sometimes seen.
Obviously if I don't know your toolset, I can't help you. I've worked with a lot of customers on a lot of different technologies. I could build something in Django, Flask, or pretty much any Python Framework, Node, Express, or pretty much any new JS frameworks, etc., Java, .Net, but if you ask for Rails, I'd have to (at the least) tell you that I don't have any recent experience in it, and I don't really love it. The better freelancers will at least try to refer you to someone else they know, but many of them might just as quickly assume that there are a million Rails freelancers out there, and you're likely to find one with the very next email.
All this, and I haven't even mentioned budget yet. People have their preferred budget ranges. Some guys like small projects, some guys prefer 3-6 month projects, etc. If you specifically mention budget, it might easily be that your budget thoughts are too small for the work at hand.
Anyway, hope this helps.