Because all of the ambition HAS to be including the actual reality of the situation and football world we live in and with even a slightest most remote chance of it being achievable mate.
NSNO is a club motto to be aspired too, not one we should think we can click our fingers and instantly achieve it whenever we so wish, it has to be worked on and at, to throw it back at people who say the club should be striving for those levels the way you're doing is IMO anyway a bit baby out with the bath water - because you don't like the way some use the motto to support there points etc.
City without doubt the most ambitious club going atm, and one who have done so with a very clear and long term plan to be the best, did so not by in 2008 hiring Guardiola or Mourinho etc, they did it by a gradual process, Hughes they left in place for one season, then Mancini (whose reputation has never been as close to Simeone for example), then Pelligrini, then finally Guardiola.
Can we get Simeone? - not a chance in hell, should we try - again i would say no, because it doesn't show ambition to try for something you know you will not be able to get, what it does is give a nice story to the press to say 'look we are ambitious' when real ambition is to go for the very best you are able to achieve at that current time - AND get them.
You seem to be of the opinion - if we can't get the very best out there, then why bother to change, my answer would be - because it's called gradual improvement, you get the best you can, that leads to the club improving, next time you go to get something then the bar for what you can attract is higher and so on and so forth.