Why do they do that? Sorry, I don't speak Spanish.
Here's a good English-language article about it, with a timeline: https://daniel.es/blog/cloudflare-vs-la-liga/
Looks like same old regulatory capture.
There are some sites that stream a pirate signal of the football matches, and they stream through Cloudflare proxied IPs. They share the IP with thousands if not millions of other sites.
When the match starts, Movistar (a big ISP, but also a TV platform that streams legally football matches) sues itself in the following terms: "we, Movistar TV, demand that Movistar ISP blocks the following IPs that are being used to stream our matches illegally", on a special and urgent procedure. The judge tells Movistar-ISP to block the IP, which they do in seconds. Now replace Movistar with the biggest ISPs in Spain, and you have more than 80% of the country with Internet capped for hours (except if you know how to use some kind of tunneling)
As the pirates share the IP with so many sites, because the IP is actually a Cloudflare proxy, a big chunk of the internet goes down. Users complains, and Movistar ask Cloudflare to block the real IP and spare the rest. Cloudflare says that they cannot legally do that as no judge actually told them to.
Our Spanish judges are historically inept when talking about copyright, internet, file sharing and similar stuff. Some of them might be more updated, but there has been cases that they ordered some publications to surrender their lithographic plates, because a cover has to be retired as late as 2007 (https://www.elmundo.es/elmundo/2007/07/20/espana/1184937587....). So I don't think they understand much more about what is an IP other than "a IP is a number assigned to a computer". And Movistar is quite happy with that.
Because LaLiga and football in general is what is governing Spain really.
to stop people pirating football streams while matches are on. Insanity
The website has a language selector on the right just below the initial screen, just FYI.
to """"""""""prevent piracy""""""""""
The football league would rather not have pirates livestream their ~90 minute games.
Pirates would rather not be blocked, so they create a new, disposable website for every game. Any blocking must happen fast.
Cloudflare would rather not block websites without a court order specifying the sites to be blocked.
The courts would rather not create a special fast lane through the courts, just to resolve a squabble between two huge corporations.