I think the pressures are from everywhere all the time. There's always a risk that something picks up enough steam to replace an OS even if it is a derivative or fork of the same OS. For C++ adoption, Linus gauged correctly that it's steam is limited and even directly taunting its supporters had low risk in a project that could challenge Linux because its set of choices over time has had many foot guns, where many developers would intentionally use what any user would consider a foot gun. As long as Linus didn't step in to define strong rules for how C++ would be used there was no likely challenger over any reasonable amount of time (for Linux/C). This is not true for rust.