Do you think the death of the more physical DT subjects could be because finding someone with the required standard of English and Maths skills, industry vocabulary and knowledge, and relevant degree, willing to work for a teaching salary is hard? Go on, speculate a bit, I'm genuinely interested in your opinion.
Finding teachers is currently difficult across all subject areas, DT is no different and it suffers from the same malady, workload, pay, behaviour, public perception, better pay in other areas for the same qualifications etc. etc. that is a huge reason
Others are that gove decided to rebuild the education system, and put pressure on schools with progress 8 and the Ebacc to go down a more academic route. Progress 8 encouraged schools to restrict the pupils that could take the subject as it sits in the bottom bucket and Ebacc encourages schools to prioritise more academic subjects.
gove then made the "vocational" subjects more academic.
He also reduced the different subject areas, RM, graphics, electronics, textiles, systems and control, engineering, food and and other associated "vocational" subjects to three areas. Technology, Engineering and Food and nutrition. Technology now encompasses everything except engineering (systems and control) and food and nutrition.
Technologies et al. are expensive subjects to run, schools budgets are reducing, and various schools are either removing the subject completely or running it as a 7 week module including drama, art, and music. then not running it as a Ks4 option.
Then you have those with the attitude that tech, art, music, drama, etc. are of little worth and encourage pupils that struggle academically in to a poor fitting subject where schools get poor results so they put less priority on getting pupils in to the subject area.
Not a huge amount of speculation in that.