In almost every Space Marine Chapter quest, players always seem to want to train up some supplementary force, the PDF of the homeworld or the serfs as some kind of elite formation and their next goal is always to start sending them out into the galaxy to help the Imperium. And I'm like 89% sure it's because that worked in the Crimson Crusaders quests.
It also totally ignores that the elite PDF forces guarding a homeworld are still less valuable/effective than the 100 Space Marines that would otherwise be on permanent garrison duty. There's nothing too bad about having some kind of supplement military force back the Chapter, but that's the job of the Guard and the Navy.
It worked that one time with the Crimson Crusaders because they were set up on a Hive World with a huge population and were capable of supplying their forces with quality equipment by themselves. They were able to send out multiple regiments of Elite troops, compared favorably to the like of the Death Korp, the Catachans, the Mordian Iron Guard, and even the Cadian Shock Troops, driven by a sense of duty instilled in them by their past and following the example set by the CC Chapter.