https://www.folklore.org/Signing_Party.html
So no "of course" about it.
Note also that Microsoft had a "no easter eggs" policy starting in the early 2000s. It's not really a Jobs thing.
"... Steve Jobs reportedly banning them in 1997 when he returned to Apple ..."
It was probably driven by the same kind of pragmatic business drivers as the later Microsoft ban, i.e. the perception by the market of how "serious" Apple was as a company.
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Edit: According to Gizmodo in 2012:
> He justified the credits ban as a way to avoid headhunters and other companies trying to poach Apple engineering talent. At a time when Apple was sinking rapidly, he said that it made no sense to make the life of the competition easier. He also argued that they were all responsible of the stuff they created in Cupertino. This was a complete change from the 1980s.