I'm not saying they should, I'm just saying that I think it makes the game worse/of no interest personally. Platforming in the first person (basically what ME is) has been unpleasant at best in each game I've experienced it in - Borderlands, Half Life, and the original ME are the three that come to mind. The problem is that we're able to move our bodies in the first person because we can rely on tactile and kinetic feedback from our feet and senses but games can't give us any of that.
Yet you still need to time and measure jumps and maneuvers correctly but without that feedback you're basically stuck with trial and error/guessing (which plays a role no matter what but I think becomes 'weighted' much more heavily), visual cues or the game having to compromise for it. Problem with visual cues in first person is, of course, that what you're able to see is limited and also influences your direction. The game could also try to account for these limits by making actions more forgiving/adding 'buffers' (bigger 'hit boxes' as it were)/templated actions (eg: 'hurdle' in BF3/BF4) but these all take away from how precise and tight the game feels and controls.
I'm sure it suits some people very nicely. I don't see how it would dumb it down though - you'd be able to see more, certainly, but I think the flipside of that is that you now could justify maybe making the 'success' window for a ledge "6 inches" instead of "12 inches" and so on and so forth. So you would 'give' the player more but also 'expect' more from them in return.