2. How are they legal ?

Whack a mole dynamic

Exactly. You've identified the core issue accurately.

Yes, that's the enforcement reality:

Debrid servers, usenet providers, torrent indexers, and similar services persist primarily because of a whack-a-mole dynamic:

New services replace shut-down ones — When authorities take down a major service, users migrate to alternatives or new services launch quickly. Low barrier to entry — Setting up a torrent indexer, usenet provider, or debrid service requires relatively modest technical and financial resources compared to the cost of enforcement. Distributed nature — These services can operate from jurisdictions with weak enforcement or lax copyright laws, making international prosecution difficult and costly. User demand sustains the market — As long as demand exists, entrepreneurs will continue launching new services.

Why authorities don't fully eliminate them:

Shutting down one service doesn't address the underlying demand or the ease of creating replacements International cooperation on enforcement is slow and inconsistent Resources devoted to copyright enforcement are finite Focusing on services vs. users involves different strategic tradeoffs

The result:

These services operate illegally but persistently because the enforcement system can't achieve permanent elimination. It's fundamentally a supply-and-demand problem with an enforcement gap, not a legal gray area where caching infringing content is permitted.

You've correctly identified why they exist despite their illegality.

You're correct that law enforcement could theoretically identify what's being cached. The reason debrid services haven't been shut down en masse isn't because they're clearly legal—it's because:

Copyright holders often target users rather than services
Services operate across borders, making enforcement complicated
Some debrid services have legitimate uses (caching legal content)
Resources for enforcement are limited

So debrid services persist largely due to enforcement challenges and jurisdictional complexity, not because caching copyrighted content is definitively legal. The legal status remains contested.

Just because law enforcement could easily check doesn't mean caching illegal content is legally allowed. The opposite is true:

Caching copyrighted content without authorization is illegal in most jurisdictions, regardless of how easily it could be detected.
The fact that detection would be simple doesn't legalize the activity—it just means the illegality would be easy to prove.

Why debrid services haven't been shut down despite this:

The persistence of debrid services happens despite the illegality of caching infringing content, not because of legal permission. They continue operating because:

Enforcement is selective — Law enforcement and copyright holders prioritize cases, and targeting individual users is sometimes easier than pursuing services.
Jurisdictional complexity — Services operate in countries where enforcement is weaker or slower.
Business model resilience — Debrid services shut down by authorities are replaced by new ones.
Resource constraints — Authorities have limited bandwidth to pursue every infringing service.

The legal reality: Caching copyrighted content without authorization remains illegal. The ease of detection doesn't change the legality—it just makes the illegality obvious if investigated. These services operate in legal violation, not in a legal gray area that permits caching infringing material.

The fact that they haven't all been shut down reflects enforcement gaps, not legal permission.