Tbh Rosaria nobles did exactly the bad move. They could knight him and give small  fief of land.  Thereby making mute any complains that he didnt get any reward for his service. At the same time he would be ruling two or three villages on the border fighting  with orc tribes being no threat to anyone.
The whole idea of Rosaria nobility don't elevate lower classes in to the ranks of  knight doesn't stand the test of history or logic.
The way Rosaria portrayed its in constant war with orcs and other creatures meaning constant casualties.
Real medieval state constantly needed more man power to feel up the ranks of professional military man.
Which get constantly depleted. The main case of loses is war attrition.
If you look in to casualties during any military campaign you will notice that majority of man died not from direct combat but through mundane diseases and  bad conditions.
And only real  mobile effective force in medieval times is knight regiments.
I recommend this article:
	
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Basically because war was so cruel, they have to Force rich peasants who had money to arm themselves and can afford horse in to position of knight and grant them low noble title.
People usually dont understand that being relatively safe peasant actually much better option then being rank and file "noble knight" Who gonna last till next battle or guaranteed till first defeat.
Again if you think its just european situation no here is the same social class in russia :
	
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Successful military carer in medieval times was a guaranteed noble title... if you survive.
And its dubious honor for many, you can gain same social position of power being merchant, in the same time you eat well, you sleep in bad and not in a harm way everyday.