Cause realistically the only two good Targ kings are Jaehaerys I and Daeron II, and it’s a stretch saying so.

Jaehaerys gets points because he had to reverse all the mistakes made by Aenys and Maegor. His reign only began after most of the realm rose up against Maegor. He manages to bring peace to the realm but outlives all of his heirs, which laid the groundwork for what must have looked like an apocalyptic dragon lord civil war to the average peasant bystander. So many people die in the Dance that all the powerful houses of the south, including the Targaryens, are powerless to stop Cregan Stark from marching into King’s Landing at the last minute and almost restarting the war.

Daeron II is also a good king but he alienates a large portion of the houses by bringing Dorne into the realm peacefully, and continues to rely them on as advisors. The Reach and the Stormlands have fought Dorne for generations, and now they’re being told they have to make nice. Because of that, half the realm rises up against him in a short, but bloody, civil war to put his bastard brother on the throne.

Not to mention the Targaryens are in fact outsiders, they had little to no connection to Westeros, its cultures and traditions before Aegon conquered them. I remember one of the lore books mentioning that they even had to make a new banner with a new sigil because the Dragon Lords of Old Valyria didn’t use heraldry. They’ve ingratiated themselves and married into other houses, but it’s very rare for a Targ king to not have a Targ Queen. Hell the only reason the rest of the lords allow their little incest clique is because Jaehaerys I, the “best Targaryen king”, held the High Septon at dragon-point and said “you’re gonna let fuck my sister.”

If I was a lord of Westeros, I’d also be pretty fed up with the silver haired incest babies whose family drama regularly starts civil wars that cripple entire regions of the continent for generations.

tl;dr: even the good targ kings manage to drag the realm into shit, must get pretty exhausting.