If someone really loves a very popular name and gives it to their child for that reason, then fair play to them, it's a good enough reason as any - but for a lot of people just loving a name isn't enough of a reason to bestow it on someone as their main identifier for the rest of their life, and that's also fair enough.
If you look back to our parents' generation, their parents were obviously influenced by the 'lovely', 'popular' names of the time - Joan, Margaret, Mary, Patricia, etc, etc. Then you look at the 'lovely' 'popular' names from our generation - Claire, Karen, Joanne, etc. The names are lovely - they must have been for enough people to choose them and make them popular.
But - all those names are dated; in some cases very dated. That's what happens with anything is popular and/or 'trendy' (for want of a less naff word). If something is very fashionable then it's inevitable that one day it will no longer be fashionable and often not just unfashionable but positively eschewed.
Nobody had my name growing up (although it is very popular now) and I loved always being the only one in my class. I also like not having a name which sounds dated to today's ears, or being Tilly X, Y or Z because there were so many of us.
I think some people find it hard to get their head around the idea that Olivia or Isabella will one day conjure up 'Margaret-like' associations for future generations.
At the moment they sound so pretty and current that it's virtually impossible to envisage them sounding fuddy-duddy and matronly, the way Margaret and Joan do to us now.
So yeah, I can totally relate to why some people want to avoid very popular (to use an un-pejorative word) names...