I think folk often use nicknames / shortened names when it is fairly clear that the person player is generally known as such in the tennis world. And that is surely perfectly reasonable.

Pretty much slam dunk re "Gabi" and no doubt re "Dan/Evo". Daniel, I think not . I guess many players simply aren't bothered about officially changing their tennis names ( I would guess when they first join the ITF, ATP, WTA etc as young players it is more natural to give their born name ).

Some may change it. Andy did from Andrew fairly early doors, Stan did it from Stanislas much more recently and plenty others, while day to day known by other names, will never bother.

And Rafael Nadal puts up with Rafa remarkably well.