No Bronze Guides, Any Reason?

I have worked on a few heads through the years where the cam was bigger and the springs stiffer than stock, running iron guides without issue.
The key word there is “few”.

I used to use iron guides in milder builds, but when the heads would come back for freshening they’d always seem to need several guides replaced..... again.
So, I pretty much just stopped using them...... and that problem went away for me.
And, yes....... I have a proper Sunnen guide hone and the Sunnen guide bore gauge to set the sizing.

An example......
Before the oval track crate motor craze, we used to build a lot of motors for the local series.
One class was allowed to run Vortec(Chevy) heads.
These were solid lifter cam motors with lifts in the .570 range. Screw in studs, guide plates, roller rockers, Ferrea 6000 series valves, etc.
We’d start out with brand new castings.
These motors would be run into the 7300rpm range.

If you just honed the guides to make sure they were straight and round, and had the correct clearance....... after one season the guides were shot.
If you just installed bronze liners right off the bat, they’d go for several years without the guides needing any attention.
These were motors that got freshened every year, so we had many examples to look at.