I belive the point being that you have to pay upkeep on anything over a hundred, so by NOT having people transfer their troops(who are under 100) people can't make continual upkeep free armies and combine at the end.
So if you want to make an army, you have to pay for it.
Also did the math, with just strat ticks(10:1) you can handle ~200 troops with just that conversion alone.(so you play crpg a lot, you can have a 200 man army with no problems)