Perhaps I'm being an idiot but are there even that many protests in the UK? This isn't America where a black person gets killed every second.
Plus, I doubt they're gonna arrest or even fine 1000+ people. That would involve a court, a jury, a judge, a defense lawyer for each person and all of that costs money.
Also, isn't the whole point of a protest to, well, protest something? You don't like something the government is doing so you oppose it.
The argument they used is that the law hadn't been updated since the 1980s and that it was outdated. In the grand scheme of things, 40 years isn't that long ago. I can't really think of what particular technologies we have now that we didn't have then that would make protests more "disruptive".