Pinterest isn't really like IG. You can't get anywhere near to follow back ratio like on Instagram.
You need to follow much more, but luckily Pinterest isn't strict as Instagram and they don't disable accounts easily like IG do. So feel free to increase your daily max for follow tool.
Also, do some repins from ordinary users, they love when someone repin their pins and it's more likely they'll follow you back.
Another tip, you're using source Followers of other accounts, right?
Try using different one. I get nice followback ratio with follow people by keyword search. However, people make make mistake here, they add keywords as: Health, Fitness, Food recipes and similar, and they end up following business accounts who never follow them back and even if they do, there's no engagement from their side.
So instead of those keywords, use female names. Yep, I said female names. Let's be honest, females are interested in stuff you're posting, not a lot of males will be interested in healthy food
So, add english female names there and follow them. This why you'll make sure you follow private accounts, not business ones.
Here's the list of names you can start with, of course, you can add some more there:
Anna, Jenna, Jennifer, Elizabeth, Amanda, Julia, Jackson, Marilyn, Sandra, Salma, Liz,