Basic economy simply isn’t worth it. They nickel and dime you with all the BS fees. And the credit card thing is total bullshit, too. They do it because they want to make sure they have your card on file in order to sell you overpriced snack boxes and charge them to your seat.
Once I had to buy a poor lady some crackers because she was on the last leg of a flight from Asia and hasn’t eaten anything, but the stewardess couldn’t take her money unless she had set up her CC ahead of time.
I fly United often enough for work that I have some status, so I’m one of the entitied snobs who board first and hog all the overhead space.
They also push their credit card with Chase. It has a $99 yearly fee, but gives you a free checked bag and lets you into Boarding Group 2 without needing extra status, which has an okay chance of having enough overhead for a carry-on. If you intend to fly United more than once in a year with a checked bag, but not enough to get status, it can make more sense to get the card.
It kind of sucks to have to play those games, but that’s Capitalism.