They know not touching
They know acoc
They are in their prime anything else is sad cope.
Rayleigh already explained this:
This is Rayleigh who's had 20+ years to ruminate over Haki/Laugh Tale/the Ancient Kingdom/History. Top-10 Haki Merchant in the series.
"But the real advancement in Haki happens during extreme use in battle. The stronger the foes you face with this power... the stronger you'll become with it."
Fighting people with stronger Haki than you WILL increase your Haki if you survive. People act like this shit is complicated, IT'S LITERALLY JUST SAIYANS FROM DRAGON BALL Z, Vegeta/Sanji jobbing until they're strong enough to stop jobbing.
So, people only max out their Haki once they stop fighting people stronger than them.
Roger and Garp must have gotten a massive Haki Bloom from fighting Domi Rocks.
This is why characters like Katakuri/King are destined to get stronger, even though they're already nearing middle-aged-status: because they stopped fighting top tiers for years, and now are finally getting pushed by the New Era.
Garp and Roger were problematic, because they kept fighting each other and making each other than much stronger post-God-Valley.
Oda's saving Prime Roger for Laugh Tale/his final fight before Laugh Tale, which I'm fine with, it makes sense to save Roger's strongest stuff for Laugh Tale.