Because teaching programming is a broad policy decision. It's exactly the sort of thing the particular department would be in charge of. If JGC had merely been suggesting a certain programming language or teaching software, then the response would have been appropriate. As it is, it sounds like they didn't understand what JGC wrote.
"Be it with Raspberry Pi computers in schools, or with some other hardware, we need to get back on top."
Rasberry Pi was just a suggestion. The broader idea of "teaching programming" was ignored.
People here will know more than most the strong history of computing that Britain has. Significant contributions to many areas of computing have come from Britain. Just computer games in the UK is a huge industry. The OP thought that there is a lack of programming experienced by young people. Other people agree; see Raspberry Pi project for an example. IT in English schools is pretty poor, there's some simplistic "How to use a word processor, how to use a spreadsheet" but nothing in depth.
Skills used in programming overlap many other areas of learning. Gather information; reduce the problem; attack each part; plan it out; step it through; iterate.
The UK has some scarily poor implementations of big IT projects. Hugely late, over budget, broken - and those are the ones that make it to completion. (Although I welcome any information about the good systems.)
We as a nation desperately need people who can program. Not just regular web / app / desktop programming, but also low quantity high quality machine shop style CNC / Pick and Place / etc manufacturing.
The fact that the department gave a useless reply is no surprise, but is disappointing.
"Be it with Raspberry Pi computers in schools, or with some other hardware, we need to get back on top."
Rasberry Pi was just a suggestion. The broader idea of "teaching programming" was ignored.