Most of the time, I'm not sure, other than toeing the legal line and simplicity, though it may be because of the kind of increased engagement they get in the social media you've seen.
In this case, they may be quoting the Victim Personal Statement where she says those exact word 'had sex with'. In that statement, the victim also labelled them as dangerous paedophiles. The court can prevent parts of a Victim Personal Statement being read into the record if it views it as inappropriate to what is being sentenced - they didn't, they allowed them to be labelled dangerous paedophiles.
In my experience, it's rare for legal professionals to use the word paedophile in court or in legal paperwork, though it absolutely happens behind closed doors and when the recording equipment is off. I work these types of cases, and it's generally framed as 'sexually attracted to minors' or 'sexually attracted to children' rather than using the word paedophile, which is a term with no legal definition so legal professionals just use whichever of those definitions is more appropriate.
Personally, I'd prefer sexually motivated by overpowering others - or a shorter term if one exists with that meaning. In most cases, I think it's more accurate. Many who do these horrors don't only do them to kids, the common thread is their enjoyment in making others cower and overpowering them, and as they get away with it, they get more extreme - to children and animals. Having dealt with many of these cases, I think most of the time (absolutely not all), the sexual motivation wasn't that their victim was a child, but that they could coerce them into it, that they could control everything. As is often said, rape is not a crime of lust, sexual assault is not about overwhelming attraction, it's a crime of power, of overpowering. I think shifting discussions on sexual crime from attraction to sexual motivation has many benefits.