As far as I was aware, and I have no more knowledge than what I read from several sources, it is as Lachlan Young says. Ilford had their chemistry manufactured for them by Tetenal, who went out of business suddenly and were not able to get back into business. Ilford had to find a new manufacturer and also took the opportunity to redesign the packaging. The powder packets are now much better for postage because they're not in cardboard boxes any more. Cheaper to mail, in the UK at least.
During the drought I bought some "D-76 substitute" from Nik & Trick, which they had manufactured for them by Bellini in Italy. It did the job though I prefer Microphen....which is thankfully back in stock and seems easy to obtain again.
Though some familiar names from the past are gone, the UK still has a significant chemical manufacturing industry. And there's nothing in those B&W developers which is in any way unusual. If I wanted, I could buy the ingredients and mix ID-11 or Microphen myself by piggybacking on an order I place in my job role as senior science technician at a secondary school. So it's not exactly as if exotic unobtanium was needed. But Ilford would want a manufacturing chemist to supply the bags of mixed chemicals, I would think. All takes a little time to arrange, hence the drought. Also, as someone pointed out above, a whiff of a supply problem and many photographers will panic buy (see also toilet roll, which was among the more stupid actions a few years ago).