Unfortunately, I have no idea why, BE ?
I'm guessing that protocols dictate, that DLM be allowed to operate untouched in order to truly stabilise the circuit. As we know, cross-talk induction from additional circuits being made live, do affect the line. You as an EU, will not have the necessary info regarding how many new live circuits have been added to the D-side cable, since your own base-line was set. I don't know if the ISP's have that info either 
(nah nah .... I do though 
) Therefore, your original speeds/stats could be quite a bit off the mark from what is truly achievable in the here and now ??
There would be meltdown if every EU were to ring and request a reset, each time DLM applied a profile cap.
Maybe there wouldn't be quite such a meltdown if an "admin" charge could be applied via the ISP, say £10 or so.
Only the really adventurous/curious would be likely to stump up (in my humble opinion), but we do know what curiosity did to the cat, don't we
As I say, this is only my guess. But I base it on the fact that even our own NGA Helpdesk operatives are told quite categorically not to perform a DLM reset adhoc, upon an engineer requesting it. There has to be a good reason for it, such as a definitive fault found and cleared. I also have that access, but have to fill a notes screen in giving reasons why I've requested an auto-reset of the DLM.
yes, I have seen that first hand when a visiting engineer did some repair work, yet the "fibre centre" point blank refused to reset DLM, arguing over the phone with him that my connection could only ever have achieved lower speed due to distance from the cabinet.
That's all in the distant past now though.
I am finally "at peace" with my stable connection, albeit at fairly low speed (28Mb to 30Mb sync speeds).
even so, curiosity about actual D-side length, cable materials, how many users are connected in my vicinity etc. just won't quite let go.
I do believe I must have been one of the first (if not THE first) to be connected via my cabinet as FTTC wasn't supposedly available via the BT checker until a few weeks after I had it installed via Plusnet.
Plusnet's checker estimated only 14.6Mb, so I suppose I shouldn't really complain but..........
18 months down the line, I imagine quite a few users may now be connected (closer to the cabinet), but living in a semi-rural area inhabited in the main by slightly less young people, I imagine not too many follow the same D-side route as mine (whatever it actually is).
Back on topic, very interesting comment from the chief engineer's publication.
If only ISP helpdesk staff could mention things like that it may save a lot of grief for bewildered end users.
Of course, providing unlocked & accessible modems may have helped too, even if on a "read only" basis for the sections that "fiddlers" could/would mess up
