The VM itself is for Claude Cowork which does all work within the VM sandbox. That doesn't help answer why they spin it up immediately and don't have a way to disable it though. Just the "why it exists" question.
If you are, obviously you need the VM.
I use Claude Code CLI myself (inside a VM, to isolate it from the host) for >90% of my needs. For the remaining fraction - email scours, cloud drive searches, other third-party connections - the desktop application is surprisingly decent. I don't even have more than half a dozen connectors enabled. In the VM I have separate, personally managed access tokens available for various third-party services. Wouldn't really try to maintain more than 5-6, otherwise it gets too confusing. [ß]
The desktop application mostly Just Works[tm] with SSO. At least when M365 doesn't suffer from their 4-times-a-day auth outage.
ß: A lot of APIs and authentication systems were designed in the stone age. You either need a 1:1 permissioned access token that can do horrendous damage, or you deal with ultra-granular, confusing and ill-designed scoping jungle where nothing makes sense. Atlassian, I'm looking at you especially. At least an MCP server, provisioned with a reasonably done service account, doesn't have all of your powers to get things wrong with.
This whole thing seems kind of silly to me I must admit. It seems obvious that Claude Desktop needs a VM for security for the majority of it's actual real world use. VM's take up memory, yeah. Them's the breaks. If other competitors have managed to provide as good (or ideally better) security scenario with less RAM, that would be interesting, but just complaining about it seems weird and uninformed to me.
Popularity here is irrelevant.
Just because the software is "popular", it does not always mean that the quality of the engineering and their choices is the best. Objectively, it's the model that everyone regards as the best rather than their desktop apps or the harness that drives it.
That is why people want to use the model and their subscription in other harnesses.
In this case, the desktop app is evidently poor with very embarrassing bugs and glitches like this and I expect well funded startups with the best engineers releasing very high quality code.
Obviously, this is not the case at Anthropic.
Claude Code itself is incredibly buggy and as we have seen the codebase is a complete mess of slop.
The answer is probably as simple as "no one thought not to do that."
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I know different people work on these things so I can't do more than guess about how engineering culture cuts across teams, but given the sheer amount of carelessness and sloppiness in Anthropic's software I have to imagine they're burning investor money in training and inference because the code to do it is as bad as the rest of their software.