If you booked through offline channels (incl. CX's own call centre and major agents such as CWT and Amex GBT), there is no ticketing deadline for DMs and (basically unlimited) companions for any kind of CX revenue (cash) booking
So DMs are only bounded by advanced purchase (be it 3, 7 or 30 days - but the majority of CX fares don't have advanced purchase anyway). Effectively you don't have to pay until the moment of OLCI. So basically DMs don't have to pay change fees as there's no need to issue revenue tickets previously until travel is 100% confirmed / at last instance, as change fees don't apply for changes before ticket issuance. For the popular CTS flights in winter as I mentioned - a lot of people utilize this benefit and 'book' themselves J / Y seats as CX revenue only releases these buckets far out while not having to issue the ticket. Then people just hold on, on, on, and chance for cheaper buckets (so C, D,... / B, H, K.. etc) to open up very close to departure and save $$$ while having a confirmed seat all along (yes, you can utilize this benefit to be confirmed in a higher fare bucket, and concurrently waitlist for lower ones). I would assume the foreseeable revenue spoilage alone for the CTS flights in winter time, given past practices, was enough to warrant a blanket shut down of this benefit across the board.

I guess CX has decided that enough is enough for abusive behavior.
I have heard stories of DMs who have
- held up to 135(!) HK-Europe seats (something like 9 pax x 15 flights), while the actual intention was for 1 (non-DM pax - as you could 'break' the itinerary and issue the ticket, so effectively this benefit extended to any companions of a DM) pax on 1 flight only
- held up a pair of I class seats on every single North Asia - HKG - SWP itinerary over a long weekend with no intention to issue and canceling <24 hours prior to departure or not at all
- tried to go-show a flight by way of redemption at HKG, was unsuccessful, then proceeded to throw a tantrum and call the CX call center to hold up dozens of seats on the same flight and leaving them empty / only released at last minute for employees

I could go on.

I personally have taken good advantage of this benefit, and I never engaged in abusive behavior like the above. I appreciate the de facto waiver of change fees as a gesture of my loyalty and business with the airline year after year. It has in turn encouraged me to stay loyal to the airline and I basically never consider other airlines flying anywhere, yes even in 2024 partly because of these 'hidden' DM benefits and especially this one. I must say I'm disappointed that CX decided to go with a blanket ban rather than impose some kind of limit (say only for DM own use or DM+1, and no more than [x] bookings at a time, or to set a deadline of say [7] days before departure, etc) - as suggested by some of my IG followers - but I guess the revenue spoilage was way too much to justify any countermeasures. And this benefit was introduced since the MPO program was set up, which was when CX was still a relatively niche (and much more premium) airline flying only trunk routes with a much smaller member base.

The second 'hidden DM benefit' is similar to this one so I won't disclose any further.
The third 'hidden DM benefit' (at least to me) is the buggy. Maybe because I'm HKG based. Lol. But I do agree that Flub (rarely seen, and often not enforced / protected properly) is a nice DM benefit too.