You're assuming that players are just purposefully throwing themselves into a meat grinder to die. They're not.
I do say that premade players often aren't on the "Upper end" of the skill bracket, because they're not. It doesn't take a genius to take a Dark knight, press salted earth, and have 3 other members of your party follow up with CC and limit breaks to literally kill everyone who got pulled in. That's not being "fed" kills. If getting caught in Salted Earth counts as feeding, then getting killed by a Ninja LB, or Samurai LB also counts as feeding. Where do you draw the line?
People who don't try are a symptom of a broken system. If its not fun, why try? Especially when the end game results give you the same roulette reward regardless of first or third. They definetely have no incentive to requeue after the roulette bonus is gone unless they're farming achievements, or tomestones. Premade players do not understand the casual player mindset, (Perhaps even the solo player mindset as well) or they just don't care, and as a result they sit here bewildered as to why they're disliked, and pointed out as one of the major reasons why people don't enjoy frontlines.
By your standards, what is trying? You say casuals "feed" premades, and they "give away free kills". It sounds like you just have no respect for these people who make up the majority of the frontlines population. It seems to me like you just don't understand the mindset of these players. You can't expect them to just "try to win" when they genuinely don't care about the end game results. They just want it to be over with, because frontlines is not fun. They're not queueing into it a second time, especially not when people run around accusing them of feeding the enemy team, not trying, and they have to face premades they don't know how to counter or deal with, and die repeatedly. Does that sound like a fun experience to you? Does that motivate you (as a casual player) to learn more about how to be a good frontlines player?