While LinkedIn was created for workers at different companies to communicate with each other, abuse of this function has led to certain changes on LinkedIn, as well as in the behavior of LinkedIn users. Messages that have confusing or opaque subjects may not even receive a look, and the same goes for a message that looks like it was sent to many users, not one in particular.
Other reasons that your LinkedIn cold message may go unread or won't elicit a response has to do with what you have to say, or whether your message follows spammy techniques that may be flagged by the in-house spam fighting system. But, keep in mind that you're cold messaging on LinkedIn, and no one is required to read or respond to your message. It happens, and the best thing that you can do is to try and learn from it and move on.