*rotation used to be compensated. It was never a truly effective way of training but we got away with it for a little while for various reasons.
For some years it inherited some of the patterns, traditions, and practices that had always been in place from the time before that were increasingly incompatible with a rotational workforce, but which took time to be dissolved before new structures, with decreasing reliance on residents to provide the full breadth of medical services (by which they actually learnt), were built to replace them.
Consultants continued, for a little while at least, to do what they had always done, and train how they had been trained, at least within the limitations of the rotational system until they 'learnt' the futility and adapted their working and training patterns.
They, accordingly, increasingly fawned over non-doctors who could be trained into imperfect but functional pattern-recognition result-regurgitation machines in a much shorter time than actually training any SHO to perform the department's operations by understanding and thinking about problems and plans, and were more consistent and reliable at taskified operations than the standard of each of the newly-arriving doctors every 4 months. As consultants were ever more squeezed, endorsing these groups over training doctors was not just desirable, but it was fundamentally the only sane business choice and the one which gave consultants the best lifestyle as well.
There were initially fewer doctors relative to training capacity in the system but also less pressure on time with more leeway to try and consciously compensate for the inadequacies of rotational training in the working day/week/month. It is now not just the norm that resident spend every available minute of their days providing low-to-no-training-value barely medical administrative tasks, but trust management and medical 'leaders' view any unused time in their working days as 'inefficiency' that could be used to improve 'flow' and 'operations', and not actually a normal and vital part of the medical job plan to be able to discuss, teach, learn, read, reflect, and troubleshoot.
Increasingly trusts and senior doctors alike realised that resident doctors were free labour that could be dumped on almost any ward to cover it with minimal investment in training... but that for providing clinics, procedure lists, outpatient clinics and other training-critical services that it made no business sense whatsoever to deliver these services with resident doctors, which would cause re-training requirements every 4-6 months and massive fluctuations in productivity in those services on a regular basis. A CNS, ACP, or PA could be trained just once, to a set standard, and to do things the way the consultant liked it 100% of the time, without any particular expertise but certainly with consistency.
Meanwhile, the 'trainee' doctors are cheap and provided by deaneries, and can be rota'd every day onto whatever ward needs a monkey without any training period, so they are. It's the only logical business plan, and no amount of 'shadowing' or 'scheduled days' in clinic or procedure lists is actually TRAINING (which requires constant regular provision of a service out of necessity to actually achieve) but is the bare minimum token excuse to feed back to deaneries and may as well just be work experience.
Rotation was already very obviously unfit for purpose come the mid-2010s when I graduated, but I then watched it all decompensate further and further over multiple years as more and more time and opportunity was sequentially stripped out of every working day, all time for informal teaching was squeezed out and made an exceptional occurrence, and formal teaching time was rationed and bean-counted down to the bare minimum acceptable to the training programmes.
And all of this, based on the fundamentally flawed foundation of an educationalist delusion that you can strip out all apprenticeship, regular exposure, consistency, trust and longitudinal assessment out and boil down all of training down to a series of uncontextualised and episodic forms, of 'assessments' and 'curriculum items', on a portfolio. You can't, and it's been a few decades of madness trying to prove that we can as the entire profession has gone to shit.