Overexposure to a name can take the shine off it. You get so used to hearing a name, it starts to sound boring.
Take Emily, for instance. It's a lovely, classic name that will never entirely go away but everyone knows girls called Emily and as such, nobody who knows anyone under the age of 30 ever comes to the name with 'fresh' ears.
Back in the '70s you were more likely to come across an Emma than an Emily. As Emma became very popular, people started looking for a name which was as nice as Emma but sounded a bit fresher. So Emily became popular. When people started to tire a little of Emily and wanted a similarly-lovely-but-fresher version, Amelia became popular, and so on.
At some point someone will say 'Emma, that's such a pretty name and you don't hear it much these days...' and the cycle will begin again.
People who post on baby name boards are either first-time parents out of touch with current trends, still thinking names like Emma and Rachel are super-popular and wondering if Emily might be a fresher alternative, or they are people with an active interest in names.
Letting a first-time parent know that Emily and Amelia are popular names is a kindness, if they thought they were being original.
If a mother-to-be is absolutely set on having a daughter named Amelia and has wanted to name her baby that since the dawn of time, it wouldn't put her off. If she and her partner were considering both Amelia and Adelaide, they might decide that Adelaide is slightly more original, despite also loving Amelia.
It's not snobbery to avoid a name that has been used so much that people can no longer see how lovely it is and just think "oh, another Sarah, how unimaginative".
(Interestingly, a Sarah born today is likely to be the only one in her class.)
As for try-hard... one of my favourite names is Cordelia (my 'fresh alternative' to Amelia, perhaps). I've seen this name dismissed as 'pretentious' and 'try-hard'. I find that strange, as it has exactly the same rhythm as Amelia and Olivia! And why is Octavia 'posh' when Olivia isn't...?
It's a minefield.