It's a step to disincentive house party goers, especially to larger gatherings. It seems there has been more in the media about the organisers being fined a large amount, I've heard of a good few £10,000 fines being handed out.
Given nights out on the town are on hold for the foreseeable, I am guessing that some people who, pre-Covid, wouldn't think much of spending a lot on a big night out (factoring in taxis as well as drinks, food etc...), may see £200 as "worth the risk" to have a night out at a party. Just for the record, I don't think like that, and wouldn't spend that much on a night out!
£800, not so much, especially given all the smart phones with cameras and videos which could result in evidence, not just from at the party itself (often through ending up on social media) but taken by people who are reporting them. I've seen quite a few of both. Initially they seemed to be mainly of students around here.
I'm not saying the police are going to be combing social media or making appeals from photos/videos/bodycam footage, but, once the images are out there, more rule breakers who were at a gathering could be identified (shopped) than the police caught at the time.