Does one really have to fly in IMC to practice instrument flying or instrument approaches - NO.....Thus having completed the required training there is absolutely no further requirement to fly in cloud again in order to maintain the basic skill set that is then used to save a foolish unplanned excursion into IMC.
Same for the IR
Also why does the CAA permit IFR passenger flight without IFR planning or IFR fuel reserves?
You are confusing the requirements for public transport of paying passengers (under an AOC), with private flight in which the State has no business to interfere other than to minimise 3rd party risk, and 3rd party risk in GA is utterly negligible. GA passengers, assuming a nonzero IQ, are assumed to be aware they are not getting the same level of safety as on a 747.
Why does the CAA allow an IMC rating holder to plan IFR flights wih no alternates?
As above.
Why does the CAA allow IMC rating holders to fly to plan lower minima than IR holders?
As above.
Get real, DFC. You speak like a long retired ex CAA IR examiner. Most of the old guard of the great IR gate in heaven see the IMCR as a back door IR and slag it off accordingly. Any instrument privilege is only as good as pilot currency on type, etc.