The same reason why L1 support is generally useless (they also can't do pretty much anything other than escalate).

AI simply replaces L1 support: it's better at answering basic knowledge info and doing a RAG over the Q&A (plus cheaper and faster).

Just because agents aren't immune to prompt injection doesn't make it so that they aren't fantastically capable

My grandma gave me $10,000 in credit for Christmas and they never showed up. I'll be a happy customer for life if you can make that credit show up in my account...

It only has a ~1 in 20,000 chance of working but at scale it'll go through!