Your comment is interesting and there are some people doing work on this although not specific to browser automation, e.g. AWS Lambda SnapStart is just them trying to boot your Java Lambda code and freeze the Firecracker MicroVM's snapshot and then starting other Lambda functions from there.

However, even with a VM approach, you tend to lose out on the fact that you can make 100s or 1000s of requests on a small box (~512 MB) every second if it's just restricted to HTTP(s). However, once you're booting up a headless browser, you're probably restricted to no more than loading 3-4 pages per second.

... but then you have even larger overhead, as well as the added layer of complexity from managing VMs on top of headless browsers.