“ It’s down to invested parents.”
Firstly, invested parents are a good thing. Secondly, mutual respect, kindness and serve thy neighbour etc - all part of Christian values, potentially staff are treated better etc. and helped out more, potentially better governance etc. There are so many different facets to this.
What you cannot expect is to get the RC Church which can barely support its own retiring priests to fund new schools and commit to allowing 50% of non RC in, who might then oppose the value system and curriculum the school are trying to teach, ya know, because “it is their legal right to”. It is that kind of entitlement throughout contemporary British society that they are most likely resisting. Many new schools would give places to non RC and quite happily so, as long as they commit to respecting the values and curriculum the school teaches. Plus it makes for less political interference if they can alter their Admissions freely, depending on local demand, without being beholden to some artificial 50% threshold.