I'm not going to claim having an explanation for all what's going on there, but coupled with reports from people who are supposed to know more than me (watched one on the other day on addiction, Internet, and sex... as applied to Spain, but still), there are some worrying observations:

• For 20 years it seemed like whatever we were doing, was working. Then, about 10 years ago, it got a hard rebound, and we still don't know about how bad the post-pandemic trend is going to look like (government officials might already have some data, though).
• Parenting since the widespread use of the touch screen (2007 and further), has changed to allow kids at ever younger ages unrestricted access to all media on the Internet. The average age to get a smartphone in Spain, has fallen from 14 to 10 years of age, with some 6 year olds already getting theirs, particularly among families with parents who are already too busy to spend time on proper parenting.
• In recent years, after a group assault got wide media coverage to the point of changing some laws, an alarming number of assaults have been reported where groups of ever younger kids (as low as 12) would target an even younger victim... then record it on video and share it.
• Social media algorithmic optimizations (like Instagram, plugged into Facebook's algorithms in 2012), have led teens down a path of addiction to sharing more and more, including bypassing age restrictions for adult content on networks like TikTok or OnlyFans (both launched 2016), where they get monetary gain from "fan service". An impactful piece was seeing a barely adult girl, after 6 months of therapy, still argue against letting go of her OnlyFans account with $3K on it, clearly made on underage content.

I would really wish it was just increased reporting, but it definitely looks like something more serious is going on.

You mentioned the 1990s, that's where I can speak from first hand experience:

• We had a hard time getting access to any porn until 18. There was some, sneaked from parents, uncles, and older brothers, but it was considered a "rare stash" that would pale in the eyes of stuff freely available to anyone with a browser and a search engine.
• "Kids would be kids", and in 6th grade we already had both the compulsive self-preasurer, and the girl who'd do "live fan service" after class. They were the odd cases out. High school is where stuff started to happen for most.
• "Social media", was going out on the street and talking to each other. Kids would talk about all sort of stuff, knowledge would always trickle down from older to younger siblings, but they were only slightly bombarded by ads to buy this or that product, not to influence how they interacted and exploit them on a massive scale.

Anyway, we could speculate a lot about what were the key changes, but since this is not supposed to be the place for such speculations, I think we can at least agree that something has changed quite dramatically.