We all know Monarch decks work.
Every turn, they generate (hopefully) a 2400 attack beater with their effect already haven gone off, removing at least one card from the field.
Functioning very basically, they use very minimal cards every turn.
They can draw upon many forms of cards for speed, as shown in the past.
Then why aren't they winning?
There are two big problems with Monarch decks.
The first one is the lack of speed. While they can draw upon several cards for speed, Monarch decks require setup, so to speak. Something needs to be fed to a monarch to summon it, and unfortunately, its not easy to get this out THEN summon a monarch right from turn 1, something needs to be on the field or graveyard in some cases to work well.
The two big "Setup" cards are, as you know, Treeborn Frog and Dandylion, but those need to be in the graveyard to activate. The next two are Spirit Reaper and Mashmallon, due to their Indestructible by battle effect. Those need to be on the field to let you turtle a bit first too.
Also in this class are Gravekeeper's Spies. Again, they are flip effects, and thus are not able to be sprung from the hand.
The exceptions of Monarch fodder to work are cards such as Jester Confit, The Tricky, and Flute of Summoning Kuriboh. Big problem with them is that they are only one time use, unlike Treeborn Frog and other cards. Thus, in the long run, you will be running a loss in advantage, which will catch up to you fast.
How decks that use this win is by pushing very hard, very fast. Summoning an additional Monarch from nowhere gives you the ability to rush your opponent, as nobody devotes too many cards to the field on turn 1. Decks like these TEND to win more often within 5 turns, and less in the longer run.
The second problem with Monarch Deck's is their predictability.
Monarch decks tend to lack many hidden tricks, with their agenda most of the time being just "summon monarch whack for 2400, spam removal". Thus, players, once they know the enemy is running a monarch deck, and has a treeborn frog in the graveyard(as an example), they can expect monarchs flying at them next turn, and thus play and set/hold cards as appropriate.
This is the part where the Kuriboh Jester and Tricky Monarchs tend to fail, despite their edge over the other variants in the first aspect.
The one decktype that succeeds here is the Quick Synchron Monarch deck, but that REALLY fails at the first part, running a very bad mid and end game, as you can use upwards four to five cards, at low two to three cards a turn.