As you genuinely seem to want some answers, this is my perspective.
It goes without saying that medicine has a hierarchical structure. The government decides how many people are needed at the top, or rather how many they are prepared to pay for - with the infrastructure that each of them requires to function effectively, beds, operating theatres, hospitals, and junior staff. However, once appointed a consultant or GP stays in post for thirty years and juniors' training has been reduced to well under ten. So while it may seem to some people (including the BMA if you take what they say at face value) that NHS workforce planning is like planting turnips, and if you plant more seeds you get more turnips, this is not the way it works.
The NHS has always required an excess of doctors in the middle grades but their relative numbers increased when their working week fell to 48hrs after the EWTD kicked in fully in 2009, and consultants' working hours were unchanged. Historically this was alleviated by IMGs who came here for training (from their perspective but provided a service from everyone else's) and then most left, which meant that UK graduates - after a longer period of training - had a reliable progression to a consultant or GP post.
The response to mounting dissatisfaction among doctors and consequently poor retention has been to expand the number of medical schools, with plans to increase qualifying doctors by a further fifty-percent, essentially throwing more fuel onto the fire.
The short answer to your immediate question is that because retention is dreadful IMGs are filling the gaps and will be required to do so in increasing numbers according to the GMC until medical school expansion catches up.
www.gmc-uk.org/-/media/documents/somep-workforce-report-2024-full-report_pdf-109169408.pdf