People don't reply because they don't feel the pain you remove. Timing is everything.
You can monitor socials for individuals complaining about the pain point or about a competitor and reach out when you got a proper "signal".
I also avoid saying things like "free trial". Instead, I offer to give them access to the paid product to try it out.
It sounds less car salesman-y and as a receiver it feels nicer to get access to a paid product rather than a free trial everyone can have. Semantics most of the time, but it helps.
You can write organic content about how to solve those pains (and hope people searching for solutions find it).
When you do get customers you should always include a form that asks _why_ they are unsubscribing. I have learned a lot from it and it also offers a chance to turn customers back around. If someone complains about the price, I can give them a discounted rate. If someone complains about a specific quality issue I can give them free credits to make up for used ones, etc.
Always respond quickly. I have landed many customers simply because I respond quickly to emails. I've had customers tell me they chose my service over "big competitor Y" because I respond to their emails (even though my service is more expensive).
If you have an entire vertical, don't undervalue the small fish. I target ~3 different types of customers and the bulk of my revenue comes from one specific type of customer. I almost got rid of the other two customers, but realized my largest customer ($1XX,XXX/year) started off as a small fish for a year before becoming a big fish.
That may go against some of the traditional advice, as the small fish tend to account for most of the support... but in my case it works out.
A lot of the small customers end up being a channel on their own. A person leaves company A and goes to company B. They introduce your product at company B because they used it at company A.
When I speak with people I always ask how they found out about my product. Nine times out of ten it's a "coworker used your product at a different company".