This isn't just a UI preference issue, it's the observability problem that every agentic system hits eventually.
When you're building agents that interact with real environments (browsers, codebases, APIs), the single hardest thing to get right isn't the model's reasoning. It's giving the operator enough visibility into what the agent is actually doing without drowning them in noise. There's a narrow band between "Read 3 files" (useless) and a full thinking trace dump (unusable), and finding it requires treating observability as a first-class design problem, not a verbosity slider.
The frustrating part is that Anthropic clearly understands this in other contexts. Their own research on agent safety talks extensively about the need for human oversight of autonomous actions. But the moment it's their own product, the instinct is to simplify away the exact information that makes oversight possible.
The people pinning to 2.1.19 aren't being difficult. They're telling you that when an agent touches my codebase, I need to know which files it read and what it searched for — not because I want to micromanage, but because that's literally the minimum viable audit trail. Take that away and you're asking users to trust a black box that edits production code.