Again, it isn't the connection speed that is a problem. Each HTTP request requires the browser to send a request to the server and wait for a response. Since there is a javascript module in front of all the css, that means that the page has to do this sequentially and not in parallel. Because of this, whatever the latency is between you and your server, you effectively add double that to each of your load requests.
So, if it takes 100ms to get to the server, that means you will have a 200ms round trip between you and your server. If you have 30 files (roughly what fbb has) that means you increase your load time by 6 seconds (you have to make the request and then wait for the server to respond). This is without even mentioning anything about file size, this is purely due to latency. Now couple this with the fact that requests aren't instantly parsed, files aren't instantly loaded on the server (or caches accessed) and all around you can see why the server would be slow.
If, on the other hand, you combined everything into 2 files, 1 for css and 1 for javascript, then you would make 2 requests (Which could be done in parallel if the javascript follows the css). With the same 100ms latency you could load the very same page in 200ms, or 400ms depending on where your js is on the page. It is a huge difference.
But it has to be noted, that even with a pretty low latency of 50ms, 30 resources will slow a page down by 3 seconds.