Developers have high incomes, but are quite frankly, extremely cheap. And I actually mean cheap and not frugal. They will spend 40 hours/week for months to save $5/mo. There's basically no logic apart from that developers have a poor concept of time and money and are spending averse (again, cheap.)
In this case, this tool is $30/mo, or about $360 / year, what is that, 3 dinners for 2 people in a year? The tool may save the developer, let's say 3-4 hours / week and at 52 * 3 or about 156 hours of savings a year. At even 30 an hour, it's saved the developer $4,680, or at 60/hour, close to $10,000, but I can guarantee that 99% of developers will not spend $30/month to make their lives easier.
My only recommendation is try to sell this product to businesses and maybe offer them a deal based on the amount of developers they have. So sell it do a dev shop with 10 developers at $20/developer / per month. Businesses understand the time/money tradeoff and are not cheap.
Developers, my only word of advice, is seriously.. stop being so cheap and spend some money to make your lives easier.