We're five points behind both of them. We're not chasing down just one team, which makes it a significantly more difficult five point gap. Especially when one of those teams also has a game in hand on us.
Arsenal have been consistently ahead of us in the table for what, a year and a half at least? Obviously much longer again in City's case. And in terms of actual performance levels they're both clearly much further along in development than us, as judged through whatever underlying stats you like or simply by watching how all three teams play. It shouldn't need explaining why both are generally considered better sides than us at the moment, not just sides who happen to be ahead of us in the table for the time being.
Or indeed why a team with City's squad in particular would be heavily favoured over a team with ours, even if we were starting the run in from an equal position. Just take a look at both teams' centre-forward options, for a start.
It's one thing to believe a mini-miracle might happen in the league, it's another to expect ETH to basically throw a game against Barcelona in an obviously much more winnable competition by fielding a second string side just for the sake of chasing that mini-miracle.