It seems to be a superhero thing: an archnemisis has to have some sort of close tie to the main character, no matter how unoriginal or contrived. The hero has to have some sort of personal reason to want to fight them: merely wanting to do so because stopping evil is in their job description isn't enough.
That's fine... for the hero's archnemesis. It's been that way forever.
But these days—say, for the past 10 years or so in the comics and ever since the Arrowverse started up on TV—that's the way it's been for
every villain. It's a trend that is tiresome and lazy and uncreative, especially given the deep bench of pre-existing characters available to choose from.
Probably the worst example I can think of from the comics is Geoff Johns' run on Green Lantern. The Sinestro Corps War was good but then after that every major storyline was about how the Guardians were shady or there was something rotten at the core of the Corps or some big secret from the Lanterns' past was coming back to haunt them. The stories weren't about the Green Lanterns patrolling the spaceways and fighting evil and defending the defenseless; they were about the inner workings of and troubles within the Corps or problems the Lanterns brought upon themselves. Got real old, real quick.
Same thing with
Arrow and
The Flash. Every season, we get another iteration of "Oh no, Oliver is/isn't/might be/doesn't want to be a killer and he pushes his team away only to welcome them back in time for the big finale." Every season, we get another iteration of "Barry is an idiot who messes things up and someone close to him ends up being the Big Bad and Barry has to defeat them by running faster than he ever has before." Now, with
Supergirl, it's 1) Kara's aunt and uncle want to take over Earth, 2) survivors from Krypton's sister world want to take over Earth, and 3) some creepy Kryptonian cult sends a baby to Earth to... apparently take it over.
I don't know about everyone else but even though I enjoyed this season of
Supergirl (not so much
Arrow and
The Flash, sort of for
Legends), I'm really ready for change.