I would say that many upper end speakers sound good, but they definitely can sound very different.
Let's say speakers that are "good" (not expensive) will have a frequency response of +/-2db.
That means that at a given frequency, there might be a 4db difference in level between speakers. That matters to me, particularly at certain frequencies. I don't know if it matters to you, but feel free to push 2000hz up 2db, then pull it down 2db and compare. Or 100hz, or anything really. Then consider that between two pairs of speakers, there might be multiple swings like that.
Add in room issues, where avoiding an extra 2db at particular frequencies might be really important.
I get your point that there are a lot of smaller speakers reviewed, which of course is due to the way samples are acquired (as has been said). I would say small speakers are a much more important resource for people starting out, who most likely will have started with some small powered speakers or a sound bar. Younger people have smaller places, and won't be going from IEMs and Edifiers to large expensive speakers in one jump. So this speaker selection bias does have some upsides.