You are asking why governments have military drafts. They happen when there aren’t enough volunteer forces, or when monetary incentives to join the army aren’t enough. America had the draft during Vietnam. If that was a contentious war (for some) and they had to introduce the draft to increase military forces, there was nothing contentious about WW2 (nazis and Japs were evil) but still, even then, they had to introduce the draft and “force people to fight”. Few will join the army out of sheer patriotism and ones that do are worth their weight in gold.
In Ukraine’s case, the number of volunteer soldiers is somewhere around 15K, maybe 20K. They get paid nothing or almost nothing, and survive on donations, or their own funds. The country is dirt poor and can’t afford to hire and provide for the hired the way it’s done in US. There are professional soldiers in Ukraine and the government only recently increased their wages.
The reason there’s no full mobilization and it’s not a “total war” situation for Ukraine is because the fighting in East Ukraine seems to be contained. If Russians advance to Odesa, Poltava or even Kyiv, number of Ukrainians voluntarily taking arms will only increase.
I guess when the war is at home or for what a person feels is in the best interests of their family and country, people are more inclined to join, and like you said, they are worth their weight in gold.
I knew a lot of guys I went to school with that were just eighteen or so, crying and scared to death of dying (which some did) because they were drafted to go fight a war in a jungle thousands of miles away for what reason they didn’t understand. And the news was telling them it was a losing war. They had plans for their young lives and it was gone.
The thing that upsets me about our wars is the rules of engagements, etc., seems to cause more casualties on our side than we should have. I’ve read that we had Vietnam won until politicos caused us to lose it.