It's not that they don't, sliding surfaces tend to, but it should be straightforward.
Interestingly most online sources show keeping the RPM up as vital for the first 1/2 hour, which is never how I started a new motor.
Must have to do with oil pressure on old V8s
Camshafts with non-roller followers only need about 30 minutes of break-in (typically at or above about 1,500rpm) of course use the cam manufacturers' recommendations. The rpm requirement is more about having the two friction surfaces wear in their normal operating environment so they don't have to endure the slow grinding at idle.
Think of it as a piece of sandpaper on a surface, if you put pressure on the sandpaper and move it fast across the surface it makes some shallow marks but if you do the same and move the sandpaper slowly across the surface you make many deeper marks.
Once the initial break-in is done (after about 30 minutes) the friction surfaces have attained their surface polish and a bit of work hardening that, in theory, will last the life of the cam and followers.
None of this is required with roller cams and followers.
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