I've personally spent around £100 - £200 on OnlyFans, as well as watch porn on a daily basis as well. I'm guessing a lot of people have the same issue as you, since I have visited cam sites as well and can see how it is addicting to spend money on it.
This is my personal take on it, but I think the way cam sites work is by creating the idea of "Make me cum by paying money", or "Get girl attention by spending money". In a way, Twitch text to speech donations are similar as well, in the idea that you get special attention.

I have learnt a technique that may be useful to reduce intrusive urges. A big mistake is to completely ignore the urge, since that will make it shout louder. Instead, you need to acknowledge that yes, you have an urge to visit porn sites. But then instead of following that thought, you need to focus on whatever you were doing at the time. So if you were working on a project, let that urge stay, but slowly bring your attention back to what you are doing. But don't push the urge out. My therapist calls this "Urge surfing", where you let it stay and it may continue to go higher. However it should eventually pass and the urge will go away. Another way to think of it is rainy weather. The rain will come, but it will also eventually go away.