Reached 100 subscribers on my mailing list - lessons learned

I've very recently reached 100 subscribers on my mailing list.

Some numbers:

• My site only has five blog posts designed to attract Google traffic.
• Overall, my site gets about 500 organic clicks per month.
• I have done zero outreach for backlinks to those blog posts.

Here are my top performing pages for the last 30 days (my five blog posts):

In my opinion, what helped to get those e-mail addresses was:

• Spending a lot of time researching and writing those blog posts. They are between 1500 and 3500 words. I'm convinced Google prefers to rank lengthy, well-thought articles.
• Adding a "free PDF resource" to every article, in exchange for the reader's e-mail.

Finally, my mistakes and lessons learned:

• I've stopped writing!
• Exactly zero of my subscribers have signed up for my SaaS (a simple keyword rank tracker). I believe the audience I was targeting in those blog posts might not be interested in what I have to offer.

I think I'll resume writing soon—and this time, I'll try to target article ideas more directly related to my product / tool.

Thanks for reading! Thoughts?