It's pure greediness when people use this type of method in gambling, they want to win by force and they lack the wisdom that doing so is exposing themselves to more risks, if gambling as less risks then this is a good method but gambling is mostly about how much you are willing to lose, because losing is more assured.
You cant generalize that those people who are betting on some different sports as pure greediness.
Which one is greedier, the one who place big bets in single bet or the one who place smaller different bets?
I wont say one of them is greedier than the other one because I have no idea the real situation of both sides, as it can be part of their own strategy while gambling.
I will say one of them is greedy if I know them personally, if I know how she/he deal with his gambling activity.
Some people place bets on multiple marches like in sports bets, and most times they almost win but because they add up too many matches one single game will destroy the whole ticket they have, I have seen this happening too many times and to me it's just complete greed, they want to win a certain amount of money in the shortest period.
I believe you are talking about parlay/multi bets, nothing wrong with it and it has nothing to do with greed, again it is a strategy to play.
Those who have small bankroll like me do like to play multi bets to get higher possible multiplier but we are ready with the consequence before placing the bets.