Probably because we're seemingly unwilling to invest in the way that the Germans have and do...
This is what bothers me so much about the Labour proposals tbh. I dug out some stats prior to the vote (or just after, one or the other) on the per capita spending in various departments, from health to welfare, and they were all considerably higher than in the mid 2000s. Yet if you listen to the rhetoric, it was all about how austerity was crippling the country, devastating public services and so on, which if that was the case then things must have been really bad in the mid 2000s when spending per capita was so much less, yet I don't recall such accusations being made at the time.
Which leads me to the point that spending money better (or differently at least) is something I have no qualms with, but that seldom seems to be on the agenda, and certainly wasn't with Labour. Instead, it was all about spending a whole lot more money, and what's more it would in all likelihood be less in the high-growth sectors you mentioned previously but in the low-growth sectors.
I've no doubt Corbyn is an honourable man who means well, but his sums are done by McDonnell who's an unabashed communist. It would be an utter disaster.