My knowledge of this comes partly from being in contact with a very large number of pilots, and partly from having been renting out my plane some years ago and seeing the sort of people who turned up wanting to fly it.
Most IMCR holders are renters or, to a smaller degree, syndicate members, and most of the latter are having constant aggro with VFR-only members who are refusing to pay for keeping going what they regard as unnecessary avionics. I would say the vast majority of syndicates that have one or more IMCR members are continually on the verge of falling apart due to this.
This does not encourage IFR currency, because currency comes from frequent flying, which (in the long run) comes only from
enjoyable flying, which in the long run rules out burger runs.
And renting has the highest marginal cost which maximally discourages currency.
I also found that almost every IR holder is already an owner. Very few exceptions. There are a very small number of IFR only syndicates, which tend to be very successful (not least because IR members will have deep pockets and tend to not bicker about trivia so much
). The remaining IR holders were mostly fakes, or lapsed IRs (most of those were instructors, spinning some great yarns, and fiddling the fuel totaliser to get reduced fuel billing), and a really miniscule # of serving airline pilots who actually liked flying IFR "GA" as well as doing it at work in jets.
So it is no wonder that IR holders tend to be so much more current. An IR is worthless unless you go places, and you can't possibly do that while renting, and you can't generally do it in a syndicate unless it is a very special amicable one o 2 or 3 members. Add to that the chunk of one's life sunk into getting an IR (any IR) which is not just a pile of truly worthless exam swatting but also 50/55 hours of hammering NDBs etc until blue in the face (knowing fully that nobody flies like that in reality). Or going to the USA to avoid the European FAA IR hassles, but that largely trades one hassle for another; more so nowadays. Then throw in the cost of a reasonable IFR plane of say £100k plus (less if you don't mind £20k Annuals) and it's no wonder IR holders are mostly a bunch of obscessive types.
most PPL/IRs make almost every flight under IFR, right through to an IAP, even when VMC, whereas most IMCR holders don't.
Funnily enough, when I once flew an ILS into Manston, in VMC, solo, I got told off by some self important instructor there who said an IAP in VMC always needs a safety pilot. I never went there after that.
The IR holder practice of always flying an IAP even under CAVOK comes from filing IFR enroute (for easy airspace access reasons, as much as anything else) and then flying an IAP is just standard ATC expectation, with a visual approach (which is an
IFR procedure anyway) being offered sometimes (if the controller can speak enough English). It also helps logging the 6/6/ FAA IR approaches. But IMCR holders cannot do this abroad...