I'm going to counterpoint a little.
Eve: I firmly believe there is an asymmetry in the understanding of how Eve works from the standpoint of laners versus the actual Eve player.
Eve is horribly vulnerable early game in high elo play. She's going to be invaded, zombie warded, and usually has very little opportunity to do anything about it. Level 2-3, No laners are warding rivers for potential junglers going into friendly jungle: They are warding the bush nearest to them, or not at all. This is 90% of high elo Eve jungle: 1 ward for 3-4 avenues of gank, loss of buffs, etc, no actual peel.
At the same time, laners don't expect to compensate for that, and counter roam, and stay to their lanes. Not only that; they PUSH their lanes. Evelynn can compensate the invades - if her laners are setting up gank opportunities. Yet, again, the majority of Eve jungled teams tend to push, depriving her of her gank, or at least ganks that would ensure a kill without dying.
So those teams screw Eve over in two ways: She's alone in her jungle vs 1-2 invaders (fun when Talon mid gets to camp her blue, while Lee Sin and Shyvana top camp her red, leaving her no chance at all to even exist), and she isn't given an opportunity to get her ganks (but the laners still want them, complain when they die to being full pushed, etc).
Then, we need to look at mid game, once lanes are moving toward the better laners and you generally know who is going to feed/has fed and who isn't. If Eve's bot loses their lane first, It's almost guaranteed Evelynn's farm is over for the rest of the game. Both her own team and the other team are going to farm her jungle, leaving her with nothing to farm. She sucks at lane farming, so while the laners have equal opportunity farming lanes/jungle, Evelynn is stuck farming 1/2 of a wave reliably, because once her Q is done, she's pretty much down to auto attacks for 6 seconds. If this happens, Eve isn't going to be worth crap until a very late game (around 30 minutes+). She won't have enough items to dive and carry (usually when this happens she might be done with her jungle item and only 1 component of a lich bane, while the other team might have 3 items on their adc), so when her team gets caught out, she more or less has to decide: stand by and watch, or go in and die too. At this point, her team has turned the game into a 4v5. in 10 minutes, when her base is almost dead, Evelynn might be able to zone and kill a couple of the other team in her own base, but the game might be over by then too.
Eve is not an effective lane pusher unless she has minions. She's not an effective baron taker, especially if she doesn't have Ravenous Hunter (She actually dies in like 3 hits without it). She's not a solo Drake taker until after about 1 1/2 items, so when she doesn't have a reliable bot..... ditto. Without a team, she's basically an occasion assassin who can lose a 28/9/19 game because she's all alone.
You'll find Assassins who rely on teams, rather than the other way around, universally fail to get 50+% win rates. The ones who teams rely on, have 60%+ win rates on players with over 200 games on that champ.
Kha: Kha is far easier to carry on. He shouldn't be in the same conversation as Evelynn, and he SHOULD be getting the kills. If he doesn't Kha will fall off, and he will become part of the lower statistic of Kha players. Kha's basic role is to nonstop gank from level 2. If he waits until 6 to gank, he's mediocre, and will scale poorly and you'll have an average team to fight against. If he's ganked the other jungler (super easy with his passive) and owns his jungle, he'll have a very early duskblade, and 5 times the lane pressure of the jungler he shut down.
But..... once late game hits..... that's where Kha's win rate plummets. After the game becomes "protect mid" and the gank opportunities dry up, so does Kha. This is especially true in late base fallen stages of the game, where, the only kills Kha can try to get, are detected and visual and grouped.
The only time Kha should be giving up kills is once he's full build. It's also very likely the adc you support him feeding kills to wouldn't use them correctly. Unless the game is a game where both the enemy and friend adc are doing well, it's very likely 10 kills won't help them. They will still run when they should be orbing or attacking, and still feed a lot more gold to the other team, since they aren't just 1/10 and worth 33g, but rather worth 450-300g. If an adc can't carry, it's better to leave them worth nothing, so that the other team starves.
And, Eve and Kha players are not ego-centric. They just know how squishy they are, how fast they die, how little they can sustain, and how much gold they are worth if they die. Asking a 4/0 Evelynn to jump into a 1v3 where the adc is 10/1 and jungler is 3/4 and support is 0/1/12 probably isn't a good idea for Eve, no matter if there's someone whose executeable or not. If Eve tries, she's likely to die before she can get that execute, and even if she does get it, the other two are going to kill her for 300g. Kha and Eve more or less also know this: they are far less effective in brawls than in solos. Kha is worthless in a team fight unless he's super fed, because his passive is off. Evelynn is a single target sniper for the most part, who also is worthless in team fights.
So.... my suggestion? Don't blame the Kha/Eve for playing smart. Play Smart yourself. Don't get caught or start fights you can't finish with/without her/him. If they see the opportunity to help, they will. But you need to create them, not expect those champs to create them for you.