Maybe because it is all a bit inconclusive. Does the growth in UK's trade with EU outstrip that of other similar economies? Is the growth higher than would have been the case if UK had remained in the EU?
I certainly don't know, but some people (no doubt with their own agendas) think the answer to both questions over the longer term is 'no'.
https://www.ft.com/content/2f63ef97-...d-4fb2e7ee9a5a
(Behind a firewall for me now, so may also be for others)
Anyway, trade impacts are only one aspect, which it seems can be argued either way depending on which data and timescales you look at. In a sense maybe I'm partly agreeing with with your second sentence. I think our international standing and reputation, the delicate political situation in NI, and our access to world leading research are also critical issues. Do you think we are in a better place now than without Brexit when you look at this bigger picture?