I've been blogging since 1996 (translation: I'm old ) and the problem with places like Substack, where you take money from people monthly or yearly, is that you never feel as if you're writing enough to justify people subscribing to you. It's one thing if you have a tip jar on your site or people make a one-time donation, but the math changes when it's a regular payment (and you want them to renew).
It's one of the (many) reasons I left Substack and just went back to my own site. I wrote about it here if you're interested: