IIRC, the Sylver A35 has facilities CAMM doesn't need (due to its launch method), to enable it to launch other missiles. This makes it bulkier & more expensive than a dedicated CAMM silo. Except for CAMM, every VLS-compatible missile the UK will use in the future (e.g. Aster 15) is too big for A35.
There is an argument for quad-packing CAMM in bigger Sylver silos, e.g. A50, which can also be used for larger missiles such as Aster 30, but that argument does not apply to A35.
If a navy has already bought A35 for other missiles, & decides to replace or supplement them with CAMM, then quad-packing it in A35 would be logical. But that does not apply to the RN.
The space & weight needed for an on-board reloading system would probably be more than it's worth. Where they were fitted, on-board VLS reloaders have been removed from ships, & none have been fitted for many years.
Reloading from a magazine needs space not only for the magazine, but also the handling equipment, & room to move the missiles & for the reloader to operate. One can fit more ready to use missiles in less space, with less weight. The only argument in favour is the distribution of weight & space, & that can be worked round by sensible design.