It seems to be almost universally agreed amongst music lovers that a loudspeaker that measures 'perfectly flat' in terms of frequency response - does not actually sound very realistic or enjoyable. Why is this so? and why can't the measurements explain why the perfect speaker doesn't sound perfect? Same with amplifiers, the perfect measuring ones can be as boring as batsh_t and do not emote.
Because most loudspeakers -- let's say the so popular 6" mid + 1" dome tweeters in a box are very poor in terms of directionality. Although flat on-axis their off-axis are not 'flat'.
Speakers designed with uniform directivity will generally be sounding correct when flat: Gedlee summa/abbey, Econowaves, Nao Note, Unity horns -- are all designed for flat response.
So measurement is not the problem. The lack or unwillingness to do complete measuremets are.