To mitigate this issue, on paper, an (usually) HR policy writes "do not do non-work related stuff with your work computer". And since many people ignore this rule, because "why have a second laptop?", the next best thing is to route all traffic from your laptop through the company, and weed out the GigHubs and GitLabs of this world (in the same manner that they block all sex-drugs-rocknroll stuff).
You can't blame a company for wanted to protect itself against a disgruntled employee that wants to push the (example - not applicable to your company) ebanking software code out in the open.
That said.. why would a person use the corporate computer for their (allow me the use of the word) 'hobby'? Unless it's for charity work, most companies don't appreciate spending resources (time, money, equipment) on other things.
Re: Chesterton's Fence - didn't know it had a name, thank you for this!