Many Parishes, Dioceses and schools are legally incorporated. Previously in the British Empire and some other countries, when Catholic organisations entered legal contracts, they HAD to call themselves “Roman Catholic” by law. This is the origin of many of the “Roman Catholic” usages that still linger on in places. They are not a sign that this is the proper name of the Church.
Of course Roman Catholic is an oxymoron. “Catholic” means universal. So what it is actually saying is the “roman” universal church.
The usage is meant to imply that there are more than one Catholic Church, which is why it was invented. When the reformation was imposed in England, most people didn’t want to change their religion, so they were told that that the new faith was the real “catholic” faith, and the faith of their fathers was “Roman” and a corrupt introduction. The peole said “we are Catholics” and the protestants said. “Yes. So are we.”
Roman Catholic is also a term meant to imply foreigness and strangeness. As in “they’re ROMAN catholics”. They’re not really normal British/American/Australian. They’re some strange group of foreigners.
To make the point: If we talked about say, the “German Baptist Church” instead of just the “Baptist Church” Would that make ordinary Britons/Americans more or less likely to join it?