First off, I think you should consider that you do not have any right or entitlement to an (I assume) unsolicited message.
I have been on both sides of the table with this. In my own work I frequently cold contact folks who I think might be relevant leads. I also cold contact folks for any number of other reasons, if only to pick their brain.
Most of those people don't respond, and that doesn't offend me! After all, they're probably very busy people. I usually try reaching out again with a shorter message to bump their inbox. It's not at all personal, and I encourage you to detach from the idea that a response has anything to do with you as a person (it may, but it is likely just as frequenly irrelevant).
Now, for my work I receive anywhere from 50-100 emails a day. This is not quite as much as the Oracle PM who also responded in this thread, but let me demonstrate why it is not feasible to respond to them all. During my day, I:
• Work, for 8 hours, between 9 and 5, with larger or smaller breaks for eating and unloading my brain. I don't have a commute because I work from home.
• Go to the gym, for an hour (not including commute, 20 minutes each way).
• Cook dinner, about an hour. Eat dinner with significant other, another hour.
• Develop a side project which may or may not become profitable in the future, a few hours.
• Watch whatever TV show I'm not caught up on, at least an hour.
• Spend miscellaneous time with my significant other, up to a few hours. May overlap with TV show.
• Sleep, at least 8 hours.
• Read social media/tech/financial/industry news, an hour or two distributed throughout the day.
...etc.
Like I said, it's not personal. I have a finite amount of time, and I'm not generally willing to compromise my time for an unsolicited message unless it's from someone I know or it's a compelling message from someone I don't.