My OF is managed without PPV after a $20 subscription; the majority of the content is sent to DMs, and I sporadically upload a photo to the main feed with the remark, “Check your messages; I sent you something.” The problem is that I’ve seen a large number of people who have never clicked on my messages. They’re missing out on a ton of content, which makes me feel horrible since I don’t want them to feel duped or anything. I’ve never received any complaints about this. My DMs receive the everyday super NSFW content and appear to just see my main feed, whereas my main feed hardly ever receives any posts and is frequently filled with pretty NSFW content. For some people, it doesn’t matter how many times I post to “check your messages.” In my bio, “CONTENT SENT TO MESSAGES” is highlighted in all caps. I have a post pinned to the top of the page that has an image that says, “Don’t forget to check your messages” and a caption that reiterates, “That’s where all the good stuff is.” Right now, I don’t know what to do. How can I just get them to read their messages? They never once opened their messages during the whole start and finish of their subscription. Edit: Since reading messages is crucial to how I manage my account, I was only explaining how I manage mine to avoid receiving comments, stating that people not reading messages is common. I’m not attempting to offer guidance on how to manage an OnlyFans account. It appeared that some took what I said as advice in the wrong direction.
I assumed you were referring to your free page, but are you actually referring to your $20 no-pay-per-view page? That’s unexpected; I’m not sure why they refuse to read their messages.
Though their messages are presumably full and go unanswered, I don’t think you should feel bad for them because they became “lame duck” subscribers, who subscribe, unsubscribe, and go on to the next creative. It’s quite difficult to keep those subscribers around.
Try addressing those particular users by name in their direct messages, such as “Hello [username]. I just wanted to remind you that content is sent to your direct messages. Feel free to ask if there’s anything you’d like to see.”
Based on what I understand, many users of Fansly and OF don’t even bother to check their messages because they are inundated with them every day from various producers (which makes sense, to be honest).
Although I don’t use PPV myself, I do send things via DMs and my feed. However, 80% are DMs.
To be honest, it’s their fault if a man subscribes but never reads his messages. Never assume 100% of your subscribers will open them! It’s okay, in my opinion, as long as at least half of them do. However, if less than 50% of your subscribers view them, be prepared to make changes.
When I ask questions like, “What’s your favorite type of content?” or “I’m filming new content today; what’s one position you want to see me in or what toy should I use?” I always get a lot of comments.
I also frequently share polls on my feed with thought-provoking subjects.
This appears to be a strange tactic. Generally, when no PPV exists, ALL contents appear in the main feed. In particular, if your current strategy isn’t even helping you, I would change it.
You can’t force someone to do anything; however, I have a lot of subscribers on my no-PPV VIP page who don’t even read the welcome message. 
They are free to do as they choose as long as they have paid!
I completely grasp why you don’t want recently signed-up users to have access to all of the content that long-standing subscribers have access to. But if they unsubscribe, I don’t care if they can still access the content! If users could keep all the content after they quit, would they be more likely to not renew? 
I have a few videos of me urging people to check their messages here. It worked for some, but not for all of them.
If you wish to keep sending all of your material via messages, try to have another network with more SFW for updates and alerts, some other network that sent notifications through subs phones. You could want to give it a try on Telegram, or it may be X, or even Instagram Stories, something that lets your subs know that something is in their inbox. People seldom have OF open all the time; hence, filling that void will help.