That is also because CPS2 was already into MAME by using a 'wrong' method. I don't think devs want to spend years on the same system.
I just hope that they put their heads together, as they did with CPS2
By wrong method you mean XOR's... Well it mite have been wrong but I think it was very effective, maby just not so much in the long term...
They were very effective, but the MAME team doesn't care about this. They only want real emulation and not a 'hacked solution', like the XORs.
That's why they now want to truly break the encryption.