It's nice enough just out of fashion. Isabelle took its place
No, no, it did not. Isabelle follows a trajectory, from late 1960s to 2010s of something like: Elizabeth / Charlotte / Chloe / Sophie / Isabelle.
Whereas Danielle is part of something like:
Jacqueline / Melanie / Danielle / Chantelle / Rochelle
In between the two is the popular, ubiquitous line of something like:
Debbie / Karen / Joanne / Sarah / Emily / Olivia
The older members of the first group, at school in the 80s/90s, are friends with Jessica, Anna, Rebecca, Catherine and Eleanor.
The second with Julie, Donna, Kay, Michelle, Gemma and Hayley.
The third with Nicola, Alison, Emma, Natalie and Rachel.
I'd concede that as some names have become uber-popular, like Charlotte / Olivia / Isabelle, then perhaps they've transcended social boundaries, so that a 'would have been Danielle' could now become an Isabelle. Danielle itself did not transcend though.
My point is that, in the UK, Danielle is not just very, very dated, in a 'had one moment of fame and is never likely to return' kind of way but also that that generation is now in their 40s and 50s, so not distant enough for nostalgia or revival and that it is linked to a particular social milieu, in a way that perhaps it isn't in France (and that Daniel certainly isn't, it's fairly classless).
I also think it can easily be pronounced in a really whiney sounding way, if called out loud, 'Dan-Yeah-ull'. I don't like that yeah sound in the middle.
Daniela is quite a different name.