Counter-terrorism, criminal investigations, national security, cybersecurity, anti-corruption, regulatory compliance, breaking up organized crime, stopping drug distribution and trafficking, stopping black market trades (weapons, human trafficking, and the aforementioned drugs), stopping production of illegal materials, preventing insider trading, detecting fraud, stopping money laundering, preventing corporate espionage, nationalistic thought-police stuff that some countries legitimately want, stopping identity theft, political back channel interference prevention, social stability (someone might incite unrest), economic stability (someone might share ideas bad for the economy), public health safety (someone might share anti-vax ideas), gang activity prevention, stopping cults and sectarian violence, scam/fraud call and message prevention, disrupting ransom schemes, preventing propaganda, stopping environmental crime, disrupting illegal immigration, military and government organization advantage against allies on whom they can spy if they pressure them into abandoning E2E... oops I mean... peacekeeping, preventing the undermining of democracy (or the fatherland/motherland for those of the authoritarian inclination). There are definitely a few bingo cards worth of possible excuses.